Fast algorithms for adaptive motion vector resolution in affine mode

ABSTRACT

A method for video processing is provided. The method includes determining, based on a coding mode of a parent coding unit of a current coding unit that uses an affine coding mode or a rate-distortion (RD) cost of the affine coding mode, a usage of an adaptive motion vector resolution (AMVR) for a conversion between a coded representation of a current block of a video and the current block; and performing the conversion according to a result of the determining.

CROSS-REFERENCE TO RELATED DOCUMENTS

This application is a continuation of International Application No.PCT/IB2019/057892, filed on Sep. 19, 2019, which claims the priority toand benefits of International Patent Application No. PCT/CN2018/106513,filed on Sep. 19, 2018, and International Patent Application No.PCT/CN2019/074433, filed on Feb. 1, 2019. All the aforementioned patentapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to video processing techniques, devices andsystems.

BACKGROUND

In spite of the advances in video compression, digital video stillaccounts for the largest bandwidth use on the internet and other digitalcommunication networks. As the number of connected user devices capableof receiving and displaying video increases, it is expected that thebandwidth demand for digital video usage will continue to grow.

SUMMARY

Devices, systems and methods related to digital video coding, andspecifically, to motion vector predictor derivation and signaling foraffine mode with adaptive motion vector resolution (AMVR) are described.The described methods may be applied to both the existing video codingstandards (e.g., High Efficiency Video Coding (HEVC)) and future videocoding standards or video codecs.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,for a conversion between a coded representation of a current block of avideo and the current block, a motion vector difference (MVD) precisionto be used for the conversion from a set of allowed multiple MVDprecisions applicable to a video region containing the current videoblock; and performing the conversion based on the MVD precision.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,for a video region comprising one or more video blocks of a video and acoded representation of the video, a usage of multiple motion vectordifference (MVD) precisions for the conversion of the one or more videoblocks in the video region; and performing the conversion based on thedetermining.

In another representative aspect, the disclosed technology may be usedto provide a method for video processing. This method includesdetermining, for a video region comprising one or more video blocks of avideo and a coded representation of the video, whether to apply anadaptive motion vector resolution (AMVR) process to a current videoblock for a conversion between the current video block and the codedrepresentation of the video; and performing the conversion based on thedetermining.

In another representative aspect, the disclosed technology may be usedto provide a method for video processing. This method includesdetermining, for a video region comprising one or more video blocks of avideo and a coded representation of the video, how to apply an adaptivemotion vector resolution (AMVR) process to a current video block for aconversion between the current video block and the coded representationof the video; and performing the conversion based on the determining.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,based on a coding mode of a parent coding unit of a current coding unitthat uses an affine coding mode or a rate-distortion (RD) cost of theaffine coding mode, a usage of an adaptive motion vector resolution(AMVR) for a conversion between a coded representation of a currentblock of a video and the current block; and performing the conversionaccording to a result of the determining.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determininga usage of an adaptive motion vector resolution (AMVR) for a conversionbetween a coded representation of a current block of a video and thecurrent block that uses an advanced motion vector prediction (AMVP)coding mode, the determining based on a rate-distortion (RD) cost of theAMVP coding mode; and performing the conversion according to a result ofthe determining.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes generating,for a conversion between a coded representation of a current block of avideo and the current block, a set of MV (Motion Vector) precisionsusing a 4-parameter affine model or 6-parameter affine model; andperforming the conversion based on the set of MV precisions.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,based on a coding mode of a parent block of a current block that uses anaffine coding mode, whether an adaptive motion vector resolution (AMVR)tool is used for a conversion, wherein the AMVR tool is used to refinemotion vector resolution during decoding; and performing the conversionaccording to a result of the determining.

In one representative aspect, the disclosed technology may be used toprovide a method for video processing. This method includes determining,based on a usage of MV precisions for previous blocks that has beenpreviously coded using an affine coding mode, a termination of arate-distortion (RD) calculations of MV precisions for a current blockthat uses the affine coding mode for a conversion between a codedrepresentation of the current block and the current block; andperforming the conversion according to a result of the determining.

In another representative aspect, the above-described method is embodiedin the form of processor-executable code and stored in acomputer-readable program medium.

In yet another representative aspect, a device that is configured oroperable to perform the above-described method is disclosed. The devicemay include a processor that is programmed to implement this method.

In yet another representative aspect, a video decoder apparatus mayimplement a method as described herein.

The above and other aspects and features of the disclosed technology aredescribed in greater detail in the drawings, the description and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of constructing a merge candidate list.

FIG. 2 shows an example of positions of spatial candidates.

FIG. 3 shows an example of candidate pairs subject to a redundancy checkof spatial merge candidates.

FIGS. 4A and 4B show examples of the position of a second predictionunit (PU) based on the size and shape of the current block.

FIG. 5 shows an example of motion vector scaling for temporal mergecandidates.

FIG. 6 shows an example of candidate positions for temporal mergecandidates.

FIG. 7 shows an example of generating a combined bi-predictive mergecandidate.

FIG. 8 shows an example of constructing motion vector predictioncandidates.

FIG. 9 shows an example of motion vector scaling for spatial motionvector candidates.

FIG. 10 shows an example of motion prediction using the alternativetemporal motion vector prediction (ATMVP) algorithm for a coding unit(CU).

FIG. 11 shows an example of a coding unit (CU) with sub-blocks andneighboring blocks used by the spatial-temporal motion vector prediction(STMVP) algorithm.

FIG. 12 shows an example flowchart for encoding with different MVprecisions.

FIGS. 13A and 13B show example snapshots of sub-block when using theoverlapped block motion compensation (OBMC) algorithm.

FIG. 14 shows an example of neighboring samples used to deriveparameters for the local illumination compensation (LIC) algorithm.

FIG. 15 shows an example of a simplified affine motion model.

FIG. 16 shows an example of an affine motion vector field (MVF) persub-block.

FIG. 17 shows an example of motion vector prediction (MVP) for theAF_INTER affine motion mode.

FIGS. 18A and 18B show examples of the 4-parameter and 6-parameteraffine models, respectively.

FIGS. 19A and 19B show example candidates for the AF_MERGE affine motionmode.

FIG. 20 shows an example of bilateral matching in pattern matched motionvector derivation (PMMVD) mode, which is a special merge mode based onthe frame-rate up conversion (FRUC) algorithm.

FIG. 21 shows an example of template matching in the FRUC algorithm.

FIG. 22 shows an example of unilateral motion estimation in the FRUCalgorithm.

FIG. 23 shows an example of an optical flow trajectory used by thebi-directional optical flow (BIO) algorithm.

FIGS. 24A and 24B show example snapshots of using of the bi-directionaloptical flow (BIO) algorithm without block extensions.

FIG. 25 shows an example of the decoder-side motion vector refinement(DMVR) algorithm based on bilateral template matching.

FIGS. 26A-26I show flowcharts of example methods for video processingbased on some implementations of the disclosed technology.

FIG. 27 is a block diagram of an example of a hardware platform forimplementing a visual media decoding or a visual media encodingtechnique described in the present document.

FIG. 28 shows an example of symmetrical mode.

FIG. 29 shows another block diagram of an example of a hardware platformfor implementing a video processing system described in the presentdocument.

DETAILED DESCRIPTION

Due to the increasing demand of higher resolution video, video codingmethods and techniques are ubiquitous in modern technology. Video codecstypically include an electronic circuit or software that compresses ordecompresses digital video, and are continually being improved toprovide higher coding efficiency. A video codec converts uncompressedvideo to a compressed format or vice versa. There are complexrelationships between the video quality, the amount of data used torepresent the video (determined by the bit rate), the complexity of theencoding and decoding algorithms, sensitivity to data losses and errors,ease of editing, random access, and end-to-end delay (latency). Thecompressed format usually conforms to a standard video compressionspecification, e.g., the High Efficiency Video Coding (HEVC) standard(also known as H.265 or MPEG-H Part 2), the Versatile Video Codingstandard to be finalized, or other current and/or future video codingstandards.

Embodiments of the disclosed technology may be applied to existing videocoding standards (e.g., HEVC, H.265) and future standards to improvecompression performance. Section headings are used in the presentdocument to improve readability of the description and do not in any waylimit the discussion or the embodiments (and/or implementations) to therespective sections only.

1. Examples of Inter-Prediction in HEVC/H.265

Video coding standards have significantly improved over the years, andnow provide, in part, high coding efficiency and support for higherresolutions. Recent standards such as HEVC and H.265 are based on thehybrid video coding structure wherein temporal prediction plus transformcoding are utilized.

1.1 Examples of Prediction Modes

Each inter-predicted PU (prediction unit) has motion parameters for oneor two reference picture lists. In some embodiments, motion parametersinclude a motion vector and a reference picture index. In otherembodiments, the usage of one of the two reference picture lists mayalso be signaled using inter_pred_idc. In yet other embodiments, motionvectors may be explicitly coded as deltas relative to predictors.

When a coding unit (CU) is coded with skip mode, one PU is associatedwith the CU, and there are no significant residual coefficients, nocoded motion vector delta or reference picture index. A merge mode isspecified whereby the motion parameters for the current PU are obtainedfrom neighboring PUs, including spatial and temporal candidates. Themerge mode can be applied to any inter-predicted PU, not only for skipmode. The alternative to merge mode is the explicit transmission ofmotion parameters, where motion vector, corresponding reference pictureindex for each reference picture list and reference picture list usageare signaled explicitly per each PU.

When signaling indicates that one of the two reference picture lists isto be used, the PU is produced from one block of samples. This isreferred to as ‘uni-prediction’. Uni-prediction is available both forP-slices and B-slices.

When signaling indicates that both of the reference picture lists are tobe used, the PU is produced from two blocks of samples. This is referredto as ‘bi-prediction’. Bi-prediction is available for B-slices only.

1.1.1 Embodiments of Constructing Candidates for Merge Mode

When a PU is predicted using merge mode, an index pointing to an entryin the merge candidates list is parsed from the bitstream and used toretrieve the motion information. The construction of this list can besummarized according to the following sequence of steps:

Step 1: Initial candidates derivation

-   -   Step 1.1: Spatial candidates derivation    -   Step 1.2: Redundancy check for spatial candidates    -   Step 1.3: Temporal candidates derivation

Step 2: Additional candidates insertion

-   -   Step 2.1: Creation of bi-predictive candidates    -   Step 2.2: Insertion of zero motion candidates

FIG. 1 shows an example of constructing a merge candidate list based onthe sequence of steps summarized above. For spatial merge candidatederivation, a maximum of four merge candidates are selected amongcandidates that are located in five different positions. For temporalmerge candidate derivation, a maximum of one merge candidate is selectedamong two candidates. Since constant number of candidates for each PU isassumed at decoder, additional candidates are generated when the numberof candidates does not reach to maximum number of merge candidate(MaxNumMergeCand) which is signalled in slice header. Since the numberof candidates is constant, index of best merge candidate is encodedusing truncated unary binarization (TU). If the size of CU is equal to8, all the PUs of the current CU share a single merge candidate list,which is identical to the merge candidate list of the 2N×2N predictionunit.

1.1.2 Constructing Spatial Merge Candidates

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 2. The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g. because it belongs to another slice or tile) or isintra coded. After candidate at position A₁ is added, the addition ofthe remaining candidates is subject to a redundancy check which ensuresthat candidates with same motion information are excluded from the listso that coding efficiency is improved.

To reduce computational complexity, not all possible candidate pairs areconsidered in the mentioned redundancy check. Instead only the pairslinked with an arrow in FIG. 3 are considered and a candidate is onlyadded to the list if the corresponding candidate used for redundancycheck has not the same motion information. Another source of duplicatemotion information is the “second PU” associated with partitionsdifferent from 2N×2N. As an example, FIGS. 4A and 4B depict the secondPU for the case of N×2N and 2N×N, respectively. When the current PU ispartitioned as N×2N, candidate at position A₁ is not considered for listconstruction. In some embodiments, adding this candidate may lead to twoprediction units having the same motion information, which is redundantto just have one PU in a coding unit. Similarly, position B₁ is notconsidered when the current PU is partitioned as 2N×N.

1.1.3 Constructing Temporal Merge Candidates

In this step, only one candidate is added to the list. Particularly, inthe derivation of this temporal merge candidate, a scaled motion vectoris derived based on co-located PU belonging to the picture which has thesmallest Picture Order Count (POC) difference with current picturewithin the given reference picture list. The reference picture list tobe used for derivation of the co-located PU is explicitly signaled inthe slice header.

FIG. 5 shows an example of the derivation of the scaled motion vectorfor a temporal merge candidate (as the dotted line), which is scaledfrom the motion vector of the co-located PU using the POC distances, tband td, where tb is defined to be the POC difference between thereference picture of the current picture and the current picture and tdis defined to be the POC difference between the reference picture of theco-located picture and the co-located picture. The reference pictureindex of temporal merge candidate is set equal to zero. For a B-slice,two motion vectors, one is for reference picture list 0 and the other isfor reference picture list 1, are obtained and combined to make thebi-predictive merge candidate.

In the co-located PU (Y) belonging to the reference frame, the positionfor the temporal candidate is selected between candidates C₀ and C₁, asdepicted in FIG. 6. If PU at position C₀ is not available, is intracoded, or is outside of the current CTU, position C₁ is used. Otherwise,position C₀ is used in the derivation of the temporal merge candidate.

1.1.4 Constructing Additional Types of Merge Candidates

Besides spatio-temporal merge candidates, there are two additional typesof merge candidates: combined bi-predictive merge candidate and zeromerge candidate. Combined bi-predictive merge candidates are generatedby utilizing spatio-temporal merge candidates. Combined bi-predictivemerge candidate is used for B-Slice only. The combined bi-predictivecandidates are generated by combining the first reference picture listmotion parameters of an initial candidate with the second referencepicture list motion parameters of another. If these two tuples providedifferent motion hypotheses, they will form a new bi-predictivecandidate.

FIG. 7 shows an example of this process, wherein two candidates in theoriginal list (710, on the left), which have mvL0 and refIdxL0 or mvL1and refIdxL1, are used to create a combined bi-predictive mergecandidate added to the final list (720, on the right).

Zero motion candidates are inserted to fill the remaining entries in themerge candidates list and therefore hit the MaxNumMergeCand capacity.These candidates have zero spatial displacement and a reference pictureindex which starts from zero and increases every time a new zero motioncandidate is added to the list. The number of reference frames used bythese candidates is one and two for uni- and bi-directional prediction,respectively. In some embodiments, no redundancy check is performed onthese candidates.

1.1.5 Examples of Motion Estimation Regions for Parallel Processing

To speed up the encoding process, motion estimation can be performed inparallel whereby the motion vectors for all prediction units inside agiven region are derived simultaneously. The derivation of mergecandidates from spatial neighborhood may interfere with parallelprocessing as one prediction unit cannot derive the motion parametersfrom an adjacent PU until its associated motion estimation is completed.To mitigate the trade-off between coding efficiency and processinglatency, a motion estimation region (MER) may be defined. The size ofthe MER may be signaled in the picture parameter set (PPS) using the“log2_parallel_merge_level_minus2” syntax element. When a MER isdefined, merge candidates falling in the same region are marked asunavailable and therefore not considered in the list construction.

1.2 Embodiments of Advanced Motion Vector Prediction (AMVP)

AMVP exploits spatio-temporal correlation of motion vector withneighboring PUs, which is used for explicit transmission of motionparameters. It constructs a motion vector candidate list by firstlychecking availability of left, above temporally neighboring PUpositions, removing redundant candidates and adding zero vector to makethe candidate list to be constant length. Then, the encoder can selectthe best predictor from the candidate list and transmit thecorresponding index indicating the chosen candidate. Similarly withmerge index signaling, the index of the best motion vector candidate isencoded using truncated unary. The maximum value to be encoded in thiscase is 2 (see FIG. 8). In the following sections, details aboutderivation process of motion vector prediction candidate are provided.

1.2.1 Examples of Constructing Motion Vector Prediction Candidates

FIG. 8 summarizes derivation process for motion vector predictioncandidate, and may be implemented for each reference picture list withrefidx as an input.

In motion vector prediction, two types of motion vector candidates areconsidered: spatial motion vector candidate and temporal motion vectorcandidate. For spatial motion vector candidate derivation, two motionvector candidates are eventually derived based on motion vectors of eachPU located in five different positions as previously shown in FIG. 2.

For temporal motion vector candidate derivation, one motion vectorcandidate is selected from two candidates, which are derived based ontwo different co-located positions. After the first list ofspatio-temporal candidates is made, duplicated motion vector candidatesin the list are removed. If the number of potential candidates is largerthan two, motion vector candidates whose reference picture index withinthe associated reference picture list is larger than 1 are removed fromthe list. If the number of spatio-temporal motion vector candidates issmaller than two, additional zero motion vector candidates is added tothe list.

1.2.2 Constructing Spatial Motion Vector Candidates

In the derivation of spatial motion vector candidates, a maximum of twocandidates are considered among five potential candidates, which arederived from PUs located in positions as previously shown in FIG. 2,those positions being the same as those of motion merge. The order ofderivation for the left side of the current PU is defined as A₀, A₁, andscaled A₀, scaled A₁. The order of derivation for the above side of thecurrent PU is defined as B₀, B₁, B₂, scaled B₀, scaled B₁, scaled B₂.For each side there are therefore four cases that can be used as motionvector candidate, with two cases not required to use spatial scaling,and two cases where spatial scaling is used. The four different casesare summarized as follows:

-   -   No spatial scaling        -   (1) Same reference picture list, and same reference picture            index (same POC)        -   (2) Different reference picture list, but same reference            picture index (same POC)    -   Spatial scaling        -   (3) Same reference picture list, but different reference            picture index (different POC)        -   (4) Different reference picture list, and different            reference picture index (different POC)

The no-spatial-scaling cases are checked first followed by the casesthat allow spatial scaling. Spatial scaling is considered when the POCis different between the reference picture of the neighbouring PU andthat of the current PU regardless of reference picture list. If all PUsof left candidates are not available or are intra coded, scaling for theabove motion vector is allowed to help parallel derivation of left andabove MV candidates. Otherwise, spatial scaling is not allowed for theabove motion vector.

As shown in the example in FIG. 9, for the spatial scaling case, themotion vector of the neighbouring PU is scaled in a similar manner asfor temporal scaling. One difference is that the reference picture listand index of current PU is given as input; the actual scaling process isthe same as that of temporal scaling.

1.2.3 Constructing Temporal Motion Vector Candidates

Apart from the reference picture index derivation, all processes for thederivation of temporal merge candidates are the same as for thederivation of spatial motion vector candidates (as shown in the examplein FIG. 6). In some embodiments, the reference picture index is signaledto the decoder.

2. Example of Inter Prediction Methods in Joint Exploration Model (JEM)

In some embodiments, future video coding technologies are explored usinga reference software known as the Joint Exploration Model (JEM). In JEM,sub-block based prediction is adopted in several coding tools, such asaffine prediction, alternative temporal motion vector prediction(ATMVP), spatial-temporal motion vector prediction (STMVP),bi-directional optical flow (BIO), Frame-Rate Up Conversion (FRUC),Locally Adaptive Motion Vector Resolution (LAMVR), Overlapped BlockMotion Compensation (OBMC), Local Illumination Compensation (LIC), andDecoder-side Motion Vector Refinement (DMVR).

2.1 Examples of Sub-CU Based Motion Vector Prediction

In the JEM with quadtrees plus binary trees (QTBT), each CU can have atmost one set of motion parameters for each prediction direction. In someembodiments, two sub-CU level motion vector prediction methods areconsidered in the encoder by splitting a large CU into sub-CUs andderiving motion information for all the sub-CUs of the large CU.Alternative temporal motion vector prediction (ATMVP) method allows eachCU to fetch multiple sets of motion information from multiple blockssmaller than the current CU in the collocated reference picture. Inspatial-temporal motion vector prediction (STMVP) method motion vectorsof the sub-CUs are derived recursively by using the temporal motionvector predictor and spatial neighbouring motion vector. In someembodiments, and to preserve more accurate motion field for sub-CUmotion prediction, the motion compression for the reference frames maybe disabled.

2.1.1 Examples of Alternative Temporal Motion Vector Prediction (ATMVP)

In the ATMVP method, the temporal motion vector prediction (TMVP) methodis modified by fetching multiple sets of motion information (includingmotion vectors and reference indices) from blocks smaller than thecurrent CU.

FIG. 10 shows an example of ATMVP motion prediction process for a CU1000. The ATMVP method predicts the motion vectors of the sub-CUs 1001within a CU 1000 in two steps. The first step is to identify thecorresponding block 1051 in a reference picture 1050 with a temporalvector. The reference picture 1050 is also referred to as the motionsource picture. The second step is to split the current CU 1000 intosub-CUs 1001 and obtain the motion vectors as well as the referenceindices of each sub-CU from the block corresponding to each sub-CU.

In the first step, a reference picture 1050 and the corresponding blockis determined by the motion information of the spatial neighboringblocks of the current CU 1000. To avoid the repetitive scanning processof neighboring blocks, the first merge candidate in the merge candidatelist of the current CU 1000 is used. The first available motion vectoras well as its associated reference index are set to be the temporalvector and the index to the motion source picture. This way, thecorresponding block may be more accurately identified, compared withTMVP, wherein the corresponding block (sometimes called collocatedblock) is always in a bottom-right or center position relative to thecurrent CU.

In the second step, a corresponding block of the sub-CU 1051 isidentified by the temporal vector in the motion source picture 1050, byadding to the coordinate of the current CU the temporal vector. For eachsub-CU, the motion information of its corresponding block (e.g., thesmallest motion grid that covers the center sample) is used to derivethe motion information for the sub-CU. After the motion information of acorresponding N×N block is identified, it is converted to the motionvectors and reference indices of the current sub-CU, in the same way asTMVP of HEVC, wherein motion scaling and other procedures apply. Forexample, the decoder checks whether the low-delay condition (e.g. thePOCs of all reference pictures of the current picture are smaller thanthe POC of the current picture) is fulfilled and possibly uses motionvector MVx (e.g., the motion vector corresponding to reference picturelist X) to predict motion vector MVy (e.g., with X being equal to 0 or 1and Y being equal to 1−X) for each sub-CU.

2.1.2 Examples of Spatial-Temporal Motion Vector Prediction (STMVP)

In the STMVP method, the motion vectors of the sub-CUs are derivedrecursively, following raster scan order. FIG. 11 shows an example ofone CU with four sub-blocks and neighboring blocks. Consider an 8×8 CU1100 that includes four 4×4 sub-CUs A (1101), B (1102), C (1103), and D(1104). The neighboring 4×4 blocks in the current frame are labelled asa (1111), b (1112), c (1113), and d (1114).

The motion derivation for sub-CU A starts by identifying its two spatialneighbors. The first neighbor is the N×N block above sub-CU A 1101(block c 1113). If this block c (1113) is not available or is intracoded the other N×N blocks above sub-CU A (1101) are checked (from leftto right, starting at block c 1113). The second neighbor is a block tothe left of the sub-CU A 1101 (block b 1112). If block b (1112) is notavailable or is intra coded other blocks to the left of sub-CU A 1101are checked (from top to bottom, staring at block b 1112). The motioninformation obtained from the neighboring blocks for each list is scaledto the first reference frame for a given list. Next, temporal motionvector predictor (TMVP) of sub-block A 1101 is derived by following thesame procedure of TMVP derivation as specified in HEVC. The motioninformation of the collocated block at block D 1104 is fetched andscaled accordingly. Finally, after retrieving and scaling the motioninformation, all available motion vectors are averaged separately foreach reference list. The averaged motion vector is assigned as themotion vector of the current sub-CU.

2.1.3 Examples of Sub-CU Motion Prediction Mode Signaling

In some embodiments, the sub-CU modes are enabled as additional mergecandidates and there is no additional syntax element required to signalthe modes. Two additional merge candidates are added to merge candidateslist of each CU to represent the ATMVP mode and STMVP mode. In otherembodiments, up to seven merge candidates may be used, if the sequenceparameter set indicates that ATMVP and STMVP are enabled. The encodinglogic of the additional merge candidates is the same as for the mergecandidates in the HM, which means, for each CU in P or B slice, two moreRD checks may be needed for the two additional merge candidates. In someembodiments, e.g., JEM, all bins of the merge index are context coded byCABAC (Context-based Adaptive Binary Arithmetic Coding). In otherembodiments, e.g., HEVC, only the first bin is context coded and theremaining bins are context by-pass coded.

2.2 Examples of Adaptive Motion Vector Difference Resolution

In some embodiments, motion vector differences (MVDs) (between themotion vector and predicted motion vector of a PU) are signalled inunits of quarter luma samples when use_integer_mv_flag is equal to 0 inthe slice header. In the JEM, a locally adaptive motion vectorresolution (LAMVR) is introduced. In the JEM, MVD can be coded in unitsof quarter luma samples, integer luma samples or four luma samples. TheMVD resolution is controlled at the coding unit (CU) level, and MVDresolution flags are conditionally signalled for each CU that has atleast one non-zero MVD components.

For a CU that has at least one non-zero MVD components, a first flag issignalled to indicate whether quarter luma sample MV precision is usedin the CU. When the first flag (equal to 1) indicates that quarter lumasample MV precision is not used, another flag is signalled to indicatewhether integer luma sample MV precision or four luma sample MVprecision is used.

When the first MVD resolution flag of a CU is zero, or not coded for aCU (meaning all MVDs in the CU are zero), the quarter luma sample MVresolution is used for the CU. When a CU uses integer-luma sample MVprecision or four-luma-sample MV precision, the MVPs in the AMVPcandidate list for the CU are rounded to the corresponding precision.

In the encoder, CU-level RD checks are used to determine which MVDresolution is to be used for a CU. That is, the CU-level RD check isperformed three times for each MVD resolution. To accelerate encoderspeed, the following encoding schemes are applied in the JEM:

-   -   During RD check of a CU with normal quarter luma sample MVD        resolution, the motion information of the current CU (integer        luma sample accuracy) is stored. The stored motion information        (after rounding) is used as the starting point for further small        range motion vector refinement during the RD check for the same        CU with integer luma sample and 4 luma sample MVD resolution so        that the time-consuming motion estimation process is not        duplicated three times.    -   RD check of a CU with 4 luma sample MVD resolution is        conditionally invoked. For a CU, when RD cost integer luma        sample MVD resolution is much larger than that of quarter luma        sample MVD resolution, the RD check of 4 luma sample MVD        resolution for the CU is skipped.

The encoding process is shown in FIG. 12. First, ¼ pel MV is tested andthe RD cost is calculated and denoted as RDCost0, then integer MV istested and the RD cost is denoted as RDCost. If RDCost1<th*RDCost0(wherein th is a positive valued threshold), then 4-pel MV is tested;otherwise, 4-pel MV is skipped. Basically, motion information and RDcost etc. are already known for ¼ pel MV when checking integer or 4-pelMV, which can be reused to speed up the encoding process of integer or4-pel MV.

2.3 Examples of Higher Motion Vector Storage Accuracy

In HEVC, motion vector accuracy is one-quarter pel (one-quarter lumasample and one-eighth chroma sample for 4:2:0 video). In the JEM, theaccuracy for the internal motion vector storage and the merge candidateincreases to 1/16 pel. The higher motion vector accuracy ( 1/16 pel) isused in motion compensation inter prediction for the CU coded withskip/merge mode. For the CU coded with normal AMVP mode, either theinteger-pel or quarter-pel motion is used.

SHVC upsampling interpolation filters, which have same filter length andnormalization factor as HEVC motion compensation interpolation filters,are used as motion compensation interpolation filters for the additionalfractional pel positions. The chroma component motion vector accuracy is1/32 sample in the JEM, the additional interpolation filters of 1/32 pelfractional positions are derived by using the average of the filters ofthe two neighbouring 1/16 pel fractional positions.

2.4 Examples of Overlapped Block Motion Compensation (OBMC)

In the JEM, OBMC can be switched on and off using syntax at the CUlevel. When OBMC is used in the JEM, the OBMC is performed for allmotion compensation (MC) block boundaries except the right and bottomboundaries of a CU. Moreover, it is applied for both the luma and chromacomponents. In the JEM, an MC block corresponds to a coding block. Whena CU is coded with sub-CU mode (includes sub-CU merge, affine and FRUCmode), each sub-block of the CU is a MC block. To process CU boundariesin a uniform fashion, OBMC is performed at sub-block level for all MCblock boundaries, where sub-block size is set equal to 4×4, as shown inFIGS. 13A and 13B.

FIG. 13A shows sub-blocks at the CU/PU boundary, and the hatchedsub-blocks are where OBMC applies. Similarly, FIG. 13B shows the sub-Pusin ATMVP mode.

When OBMC applies to the current sub-block, besides current motionvectors, motion vectors of four connected neighboring sub-blocks, ifavailable and are not identical to the current motion vector, are alsoused to derive prediction block for the current sub-block. Thesemultiple prediction blocks based on multiple motion vectors are combinedto generate the final prediction signal of the current sub-block.

Prediction block based on motion vectors of a neighboring sub-block isdenoted as PN, with N indicating an index for the neighboring above,below, left and right sub-blocks and prediction block based on motionvectors of the current sub-block is denoted as PC. When PN is based onthe motion information of a neighboring sub-block that contains the samemotion information to the current sub-block, the OBMC is not performedfrom PN. Otherwise, every sample of PN is added to the same sample inPC, i.e., four rows/columns of PN are added to PC. The weighting factors{¼, ⅛, 1/16, 1/32} are used for PN and the weighting factors {¾, ⅞,15/16, 31/32} are used for PC. The exception are small MC blocks, (i.e.,when height or width of the coding block is equal to 4 or a CU is codedwith sub-CU mode), for which only two rows/columns of PN are added toPC. In this case weighting factors {¼, ⅛} are used for PN and weightingfactors {¾, ⅞} are used for PC. For PN generated based on motion vectorsof vertically (horizontally) neighboring sub-block, samples in the samerow (column) of PN are added to PC with a same weighting factor.

In the JEM, for a CU with size less than or equal to 256 luma samples, aCU level flag is signaled to indicate whether OBMC is applied or not forthe current CU. For the CUs with size larger than 256 luma samples ornot coded with AMVP mode, OBMC is applied by default. At the encoder,when OBMC is applied for a CU, its impact is taken into account duringthe motion estimation stage. The prediction signal formed by OBMC usingmotion information of the top neighboring block and the left neighboringblock is used to compensate the top and left boundaries of the originalsignal of the current CU, and then the normal motion estimation processis applied.

2.5 Examples of Local Illumination Compensation (LIC)

LIC is based on a linear model for illumination changes, using a scalingfactor a and an offset b. And it is enabled or disabled adaptively foreach inter-mode coded coding unit (CU).

When LIC applies for a CU, a least square error method is employed toderive the parameters a and b by using the neighboring samples of thecurrent CU and their corresponding reference samples. FIG. 14 shows anexample of neighboring samples used to derive parameters of the ICalgorithm. Specifically, and as shown in FIG. 14, the subsampled (2:1subsampling) neighbouring samples of the CU and the correspondingsamples (identified by motion information of the current CU or sub-CU)in the reference picture are used. The IC parameters are derived andapplied for each prediction direction separately.

When a CU is coded with merge mode, the LIC flag is copied fromneighboring blocks, in a way similar to motion information copy in mergemode; otherwise, an LIC flag is signaled for the CU to indicate whetherLIC applies or not.

When LIC is enabled for a picture, an additional CU level RD check isneeded to determine whether LIC is applied or not for a CU. When LIC isenabled for a CU, the mean-removed sum of absolute difference (MR-SAD)and mean-removed sum of absolute Hadamard-transformed difference(MR-SATD) are used, instead of SAD and SATD, for integer pel motionsearch and fractional pel motion search, respectively.

To reduce the encoding complexity, the following encoding scheme isapplied in the JEM:

-   -   LIC is disabled for the entire picture when there is no obvious        illumination change between a current picture and its reference        pictures. To identify this situation, histograms of a current        picture and every reference picture of the current picture are        calculated at the encoder. If the histogram difference between        the current picture and every reference picture of the current        picture is smaller than a given threshold, LIC is disabled for        the current picture; otherwise, LIC is enabled for the current        picture.

2.6 Examples of Affine Motion Compensation Prediction

In HEVC, only a translation motion model is applied for motioncompensation prediction (MCP). However, the camera and objects may havemany kinds of motion, e.g. zoom in/out, rotation, perspective motions,and/or other irregular motions. JEM, on the other hand, applies asimplified affine transform motion compensation prediction. FIG. 15shows an example of an affine motion field of a block 1400 described bytwo control point motion vectors V₀ and V₁. The motion vector field(MVF) of the block 1400 can be described by the following equation:

$\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

As shown in FIG. 15, (v_(0x), v_(0y)) is motion vector of the top-leftcorner control point, and (v_(1x), v_(1y)) is motion vector of thetop-right corner control point. To simplify the motion compensationprediction, sub-block based affine transform prediction can be applied.The sub-block size M×N is derived as follows:

$\begin{matrix}\left\{ \begin{matrix}{M = {{clip}\; 3\left( {4,w,\frac{w \times {MvPre}}{\max \left( {{{abs}\left( {v_{1x} - v_{0x}} \right)},{{abs}\left( {v_{1y} - v_{0y}} \right)}} \right)}} \right)}} \\{N = {{clip}\; 3\left( {4,h,\frac{h \times {MvPre}}{\max \left( {{{abs}\left( {v_{2x} - v_{0x}} \right)},{{abs}\left( {v_{2y} - v_{0y}} \right)}} \right)}} \right)}}\end{matrix} \right. & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

Here, MvPre is the motion vector fraction accuracy (e.g., 1/16 in JEM).(v_(2x), v_(2y)) is motion vector of the bottom-left control point,calculated according to Eq. (1). M and N can be adjusted downward ifnecessary to make it a divisor of w and h, respectively.

FIG. 16 shows an example of affine MVF per sub-block for a block 1500.To derive motion vector of each M×N sub-block, the motion vector of thecenter sample of each sub-block can be calculated according to Eq. (1),and rounded to the motion vector fraction accuracy (e.g., 1/16 in JEM).Then the motion compensation interpolation filters can be applied togenerate the prediction of each sub-block with derived motion vector.After the MCP, the high accuracy motion vector of each sub-block isrounded and saved as the same accuracy as the normal motion vector.

2.6.1 Embodiments of the AF_INTER Mode

In the JEM, there are two affine motion modes: AF_INTER mode andAF_MERGE mode. For CUs with both width and height larger than 8,AF_INTER mode can be applied. An affine flag in CU level is signaled inthe bitstream to indicate whether AF_INTER mode is used. In the AF_INTERmode, a candidate list with motion vector pair {(v₀, v₁)v₀={v_(A),v_(B), v_(C)}, v₁={v_(D),v_(E)}} is constructed using the neighboringblocks.

FIG. 17 shows an example of motion vector prediction (MVP) for a block1600 in the AF_INTER mode. As shown in FIG. 17, v₀ is selected from themotion vectors of the sub-block A, B, or C. The motion vectors from theneighboring blocks can be scaled according to the reference list. Themotion vectors can also be scaled according to the relationship amongthe Picture Order Count (POC) of the reference for the neighboringblock, the POC of the reference for the current CU, and the POC of thecurrent CU. The approach to select v₁ from the neighboring sub-block Dand E is similar. If the number of candidate list is smaller than 2, thelist is padded by the motion vector pair composed by duplicating each ofthe AMVP candidates. When the candidate list is larger than 2, thecandidates can be firstly sorted according to the neighboring motionvectors (e.g., based on the similarity of the two motion vectors in apair candidate). In some implementations, the first two candidates arekept. In some embodiments, a Rate Distortion (RD) cost check is used todetermine which motion vector pair candidate is selected as the controlpoint motion vector prediction (CPMVP) of the current CU. An indexindicating the position of the CPMVP in the candidate list can besignaled in the bitstream. After the CPMVP of the current affine CU isdetermined, affine motion estimation is applied and the control pointmotion vector (CPMV) is found. Then the difference of the CPMV and theCPMVP is signaled in the bitstream.

In AF_INTER mode, when 4/6 parameter affine mode is used, 2/3 controlpoints are required, and therefore 2/3 MVD needs to be coded for thesecontrol points, as shown in FIGS. 18A and 18B. In an existingimplementation, the MV may be derived as follows, e.g., it predicts mvd₁and mvd₂ from mvd₀.

mv ₀ =mv ₀ +mvd ₀

mv ₁ =mv ₁ +mvd ₁ +mvd ₀

mv ₂ =mv ₂ +mvd ₂ +mvd ₀

Herein, mv _(i), mvd₁ and mv₁ are the predicted motion vector, motionvector difference and motion vector of the top-left pixel (i=0),top-right pixel (i=1) or left-bottom pixel (i=2) respectively, as shownin FIG. 18B. In some embodiments, the addition of two motion vectors(e.g., mvA(xA, yA) and mvB(xB, yB)) is equal to summation of twocomponents separately. For example, newMV=mvA+mvB implies that the twocomponents of newMV are set to (xA+xB) and (yA+yB), respectively.

2.6.2 Examples of Fast Affine ME Algorithms in AF_INTER Mode

In some embodiments of the affine mode, MV of 2 or 3 control pointsneeds to be determined jointly. Directly searching the multiple MVsjointly is computationally complex. In an example, a fast affine MEalgorithm is proposed and is adopted into VTM/BMS.

For example, the fast affine ME algorithm is described for the4-parameter affine model, and the idea can be extended to 6-parameteraffine model:

$\begin{matrix}\left\{ \begin{matrix}{x^{\prime} = {{ax} + {by} + c}} \\{y^{\prime} = {{- {bx}} + {ay} + d}}\end{matrix} \right. & {{Eq}.\mspace{14mu} (3)} \\\left\{ \begin{matrix}{{mv}_{({x,y})}^{h} = {{x^{\prime} - x} = {{\left( {a - 1} \right)x} + {by} + c}}} \\{{mv}_{({x,y})}^{v} = {{y^{\prime} - y} = {{- {bx}} + {\left( {a - 1} \right)y} + d}}}\end{matrix} \right. & {{Eq}.\mspace{14mu} (4)}\end{matrix}$

Replacing (a−1) with a′ enables the motion vectors to be rewritten as:

$\begin{matrix}\left\{ \begin{matrix}{{mv}_{({x,y})}^{h} = {{x^{\prime} - x} = {{a^{\prime}x} + {by} + c}}} \\{{mv}_{({x,y})}^{v} = {{y^{\prime} - y} = {{- {bx}} + {a^{\prime}y} + d}}}\end{matrix} \right. & {{Eq}.\mspace{14mu} (5)}\end{matrix}$

If it is assumed that the motion vectors of the two controls points (0,0) and (0, w) are known, from Equation (5) the affine parameters may bederived as:

$\begin{matrix}\left\{ {\begin{matrix}{c = {mv}_{({0,0})}^{h}} \\{d = {mv}_{({0,0})}^{v}}\end{matrix}.} \right. & {{Eq}.\mspace{14mu} (6)}\end{matrix}$

The motion vectors can be rewritten in vector form as:

MV(p)=A(P)*MV _(C) ^(T).  Eq. (7)

Herein, P=(x, y) is the pixel position,

$\begin{matrix}{{{A(P)} = \begin{bmatrix}1 & x & 0 & y \\0 & y & 1 & {- x}\end{bmatrix}},{and}} & {{Eq}.\mspace{14mu} (8)} \\{{MV}_{c} = {\begin{bmatrix}{mv}_{({0,0})}^{h} & a & {mv}_{({0,0})}^{v} & b\end{bmatrix}.}} & {{Eq}.\mspace{14mu} (9)}\end{matrix}$

In some embodiments, and at the encoder, the MVD of AF_INTER may bederived iteratively. Denote MV^(i)(P) as the MV derived in the ithiteration for position P and denote dMV_(C) ^(i) as the delta updatedfor MV_(C) in the ith iteration. Then in the (i+1)th iteration,

$\begin{matrix}\begin{matrix}{{{MV}^{\mspace{11mu} {i + 1}}(P)} = {{A(P)}*\left( {\left( {MV}_{C}^{i} \right)^{T} + \left( {dMV}_{C}^{i} \right)^{T}} \right)}} \\{= {{{A(P)}*\left( {MV}_{C}^{i} \right)^{T}} + {{A(P)}*\left( {dMV}_{C}^{i} \right)^{T}}}} \\{= {{{MV}^{\mspace{11mu} i}(P)} + {{A(P)}*{\left( {dMV}_{C}^{i} \right)^{T}.}}}}\end{matrix} & {{Eq}.\mspace{14mu} (10)}\end{matrix}$

Denote Pic_(ref) as the reference picture and denote Pic_(cur) as thecurrent picture and denote Q=P+MV^(i)(P). If the MSE is used as thematching criterion, then the function that needs to be minimized may bewritten as:

$\begin{matrix}{{\min {\sum\limits_{P}\left( {{{Pic}_{cur}(P)} - {{Pic}_{ref}\left( {P + {{MV}^{i + 1}(P)}} \right)}} \right)^{2}}} = {\min {\sum\limits_{P}\left( {{{Pic}_{cur}(P)} - {{Pic}_{ref}\left( {Q + {{A(P)}*\left( {dMV}_{c}^{i} \right)^{T}}} \right)}} \right)^{2}}}} & {{Eq}.\mspace{14mu} (11)}\end{matrix}$

If it is assumed that (dMV_(C) ^(i))^(T) is small enough,Pic_(ref)(Q+A(P)*(dMV_(C) ^(i))^(T)) may be rewritten, as anapproximation based on a 1-st order Taylor expansion, as:

$\begin{matrix}{{{Pic}_{ref}\left( {Q + {{A(P)}*\left( {dMV}_{C}^{i} \right)^{T}}} \right)} \approx {{{Pic}_{ref}(Q)} + {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*{\left( {dMV}_{C}^{i} \right)^{T}.}}}} & (12) \\{\mspace{79mu} {{{Herein},\mspace{20mu} {{{Pic}_{ref}^{\prime}(Q)} = {{{\left\lbrack {\frac{{dPic}_{ref}(Q)}{dx}\frac{{dPic}_{ref}(Q)}{dy}} \right\rbrack.\mspace{20mu} {If}}\mspace{14mu} {the}\mspace{14mu} {notation}\mspace{14mu} {E^{i + 1}(P)}} = {{{Pic}_{cur}(P)} - {{{Pic}_{ref}(Q)}\mspace{14mu} {is}}}}}}\text{}\mspace{20mu} {{adopted},{{then}\text{:}}}{{\min {\sum\limits_{P}\left( {{{Pic}_{cur}(P)} - {{Pic}_{ref}(Q)} - {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*\left( {dMV}_{C}^{i} \right)^{T}}} \right)^{2}}} = {\min {\sum\limits_{P}\left( {{E^{i + 1}(P)} - {{{Pic}_{ref}^{\prime}(Q)}*{A(P)}*\left( {dMV}_{C}^{i} \right)^{T}}} \right)^{2}}}}}} & {{Eq}.\mspace{14mu} (13)}\end{matrix}$

The term dMV_(C) may be derived by setting the derivative of the errorfunction to zero, and then computing delta MV of the control points (0,0) and (0, w) according to A(P)*(dMV_(C) ^(i))^(T), as follows:

dMV _((0,0)) ^(h) =dMV _(C) ^(i)[0]  Eq. (14)

dMV _((0,w)) ^(h) =dMV _(C) ^(i)[1]*w+dMV _(C) ^(i)[2]  Eq. (15)

dMV _((0,0)) ^(v) =dMV _(C) ^(i)[2]  Eq. (16)

dMV _((0,W)) ^(v) =−dMV _(C) ^(i)[3]*w+dMV _(C) ^(i)[2]  Eq. (17)

In some embodiments, this MVD derivation process may be iterated ntimes, and the final MVD may be calculated as follows:

fdMV _((0,0)) ^(h)=Σ_(i=0) ^(n-1) dMV _(C) ^(i)[0]  Eq. (18)

fdMV _((0,w)) ^(h)=Σ_(i=0) ^(n-1) dMV _(C) ^(i)[1]*w+Σ _(i=0) ^(n-1) dMV_(C) ^(i)[0]  Eq. (19)

fdMV _((0,0)) ^(v)=Σ_(i=0) ^(n-1) dMV _(C) ^(i)[2]  Eq. (20)

fdMV _((0,w)) ^(v)=Σ_(i=0) ^(n-1) dMV _(C) ^(i)[3]*w+Σ _(i=0) ^(n-1) dMV_(C) ^(i)[2]  Eq. (21)

In the aforementioned implementation, predicting delta MV of controlpoint (0, w), denoted by mvd₁ from delta MV of control point (0, 0),denoted by mvd₀, results in only (Σ_(i=0) ^(n-1)dMV_(C) ^(i)[1]*w,−Σ_(i=0) ^(n-1)−dMV_(C) ^(i)[3]*w) being encoded for mvd₁.

2.6.3 Embodiments of the AF_MERGE Mode

When a CU is applied in AF_MERGE mode, it gets the first block codedwith an affine mode from the valid neighboring reconstructed blocks.FIG. 19A shows an example of the selection order of candidate blocks fora current CU 1800. As shown in FIG. 19A, the selection order can be fromleft (1801), above (1802), above right (1803), left bottom (1804) toabove left (1805) of the current CU 1800. FIG. 19B shows another exampleof candidate blocks for a current CU 1800 in the AF_MERGE mode. If theneighboring left bottom block 1801 is coded in affine mode, as shown inFIG. 19B, the motion vectors v₂, v₃ and v₄ of the top left corner, aboveright corner, and left bottom corner of the CU containing the sub-block1801 are derived. The motion vector v₀ of the top left corner on thecurrent CU 1800 is calculated based on v2, v3 and v4. The motion vectorv1 of the above right of the current CU can be calculated accordingly.

After the CPMV of the current CU v₀ and v₁ are computed according to theaffine motion model in Eq. (1), the MVF of the current CU can begenerated. In order to identify whether the current CU is coded withAF_MERGE mode, an affine flag can be signaled in the bitstream whenthere is at least one neighboring block is coded in affine mode.

2.7 Examples of Pattern Matched Motion Vector Derivation (PMMVD)

The PMMVD mode is a special merge mode based on the Frame-Rate UpConversion (FRUC) method. With this mode, motion information of a blockis not signaled but derived at decoder side.

A FRUC flag can be signaled for a CU when its merge flag is true. Whenthe FRUC flag is false, a merge index can be signaled and the regularmerge mode is used. When the FRUC flag is true, an additional FRUC modeflag can be signaled to indicate which method (e.g., bilateral matchingor template matching) is to be used to derive motion information for theblock.

At the encoder side, the decision on whether using FRUC merge mode for aCU is based on RD cost selection as done for normal merge candidate. Forexample, multiple matching modes (e.g., bilateral matching and templatematching) are checked for a CU by using RD cost selection. The oneleading to the minimal cost is further compared to other CU modes. If aFRUC matching mode is the most efficient one, FRUC flag is set to truefor the CU and the related matching mode is used.

Typically, motion derivation process in FRUC merge mode has two steps: aCU-level motion search is first performed, then followed by a Sub-CUlevel motion refinement. At CU level, an initial motion vector isderived for the whole CU based on bilateral matching or templatematching. First, a list of MV candidates is generated and the candidatethat leads to the minimum matching cost is selected as the startingpoint for further CU level refinement. Then a local search based onbilateral matching or template matching around the starting point isperformed. The MV results in the minimum matching cost is taken as theMV for the whole CU. Subsequently, the motion information is furtherrefined at sub-CU level with the derived CU motion vectors as thestarting points.

For example, the following derivation process is performed for a W×H CUmotion information derivation. At the first stage, MV for the whole W×HCU is derived. At the second stage, the CU is further split into M×Msub-CUs. The value of M is calculated as in Eq. (22), D is a predefinedsplitting depth which is set to 3 by default in the JEM. Then the MV foreach sub-CU is derived.

$\begin{matrix}{M = {\max \left\{ {4,{\min \left\{ {\frac{M}{2^{D}},\frac{N}{2^{D}}} \right\}}} \right\}}} & {{Eq}.\mspace{14mu} (22)}\end{matrix}$

FIG. 20 shows an example of bilateral matching used in the Frame-Rate UpConversion (FRUC) method. The bilateral matching is used to derivemotion information of the current CU by finding the closest matchbetween two blocks along the motion trajectory of the current CU (1900)in two different reference pictures (1910, 1911). Under the assumptionof continuous motion trajectory, the motion vectors MV0 (1901) and MV1(1902) pointing to the two reference blocks are proportional to thetemporal distances, e.g., TD0 (1903) and TD1 (1904), between the currentpicture and the two reference pictures. In some embodiments, when thecurrent picture 1900 is temporally between the two reference pictures(1910, 1911) and the temporal distance from the current picture to thetwo reference pictures is the same, the bilateral matching becomesmirror based bi-directional MV.

FIG. 21 shows an example of template matching used in the Frame-Rate UpConversion (FRUC) method. Template matching can be used to derive motioninformation of the current CU 2000 by finding the closest match betweena template (e.g., top and/or left neighboring blocks of the current CU)in the current picture and a block (e.g., same size to the template) ina reference picture 2010. Except the aforementioned FRUC merge mode, thetemplate matching can also be applied to AMVP mode. In both JEM andHEVC, AMVP has two candidates. With the template matching method, a newcandidate can be derived. If the newly derived candidate by templatematching is different to the first existing AMVP candidate, it isinserted at the very beginning of the AMVP candidate list and then thelist size is set to two (e.g., by removing the second existing AMVPcandidate). When applied to AMVP mode, only CU level search is applied.

The MV candidate set at CU level can include the following: (1) originalAMVP candidates if the current CU is in AMVP mode, (2) all mergecandidates, (3) several MVs in the interpolated MV field (describedlater), and top and left neighboring motion vectors.

When using bilateral matching, each valid MV of a merge candidate can beused as an input to generate a MV pair with the assumption of bilateralmatching. For example, one valid MV of a merge candidate is (MVa,ref_(a)) at reference list A. Then the reference picture ref_(b) of itspaired bilateral MV is found in the other reference list B so thatref_(a) and ref_(b) are temporally at different sides of the currentpicture. If such a ref_(b) is not available in reference list B, ref_(b)is determined as a reference which is different from ref_(a) and itstemporal distance to the current picture is the minimal one in list B.After ref_(b) is determined, MVb is derived by scaling MVa based on thetemporal distance between the current picture and ref_(a), ref_(b).

In some implementations, four MVs from the interpolated MV field canalso be added to the CU level candidate list. More specifically, theinterpolated MVs at the position (0, 0), (W/2, 0), (0, H/2) and (W/2,H/2) of the current CU are added. When FRUC is applied in AMVP mode, theoriginal AMVP candidates are also added to CU level MV candidate set. Insome implementations, at the CU level, 15 MVs for AMVP CUs and 13 MVsfor merge CUs can be added to the candidate list.

The MV candidate set at sub-CU level includes an MV determined from aCU-level search, (2) top, left, top-left and top-right neighboring MVs,(3) scaled versions of collocated MVs from reference pictures, (4) oneor more ATMVP candidates (e.g., up to four), and (5) one or more STMVPcandidates (e.g., up to four). The scaled MVs from reference picturesare derived as follows. The reference pictures in both lists aretraversed. The MVs at a collocated position of the sub-CU in a referencepicture are scaled to the reference of the starting CU-level MV. ATMVPand STMVP candidates can be the four first ones. At the sub-CU level,one or more MVs (e.g., up to 17) are added to the candidate list.

Generation of an interpolated MV field. Before coding a frame,interpolated motion field is generated for the whole picture based onunilateral ME. Then the motion field may be used later as CU level orsub-CU level MV candidates.

In some embodiments, the motion field of each reference pictures in bothreference lists is traversed at 4×4 block level. FIG. 22 shows anexample of unilateral Motion Estimation (ME) 2100 in the FRUC method.For each 4×4 block, if the motion associated to the block passingthrough a 4×4 block in the current picture and the block has not beenassigned any interpolated motion, the motion of the reference block isscaled to the current picture according to the temporal distance TD0 andTD1 (the same way as that of MV scaling of TMVP in HEVC) and the scaledmotion is assigned to the block in the current frame. If no scaled MV isassigned to a 4×4 block, the block's motion is marked as unavailable inthe interpolated motion field.

Interpolation and matching cost. When a motion vector points to afractional sample position, motion compensated interpolation is needed.To reduce complexity, bi-linear interpolation instead of regular 8-tapHEVC interpolation can be used for both bilateral matching and templatematching.

The calculation of matching cost is a bit different at different steps.When selecting the candidate from the candidate set at the CU level, thematching cost can be the absolute sum difference (SAD) of bilateralmatching or template matching. After the starting MV is determined, thematching cost C of bilateral matching at sub-CU level search iscalculated as follows:

C=SAD+w·(|MV _(x) −MV _(x) ^(s) |+|MV _(y) −MV _(y) ^(s)|)  Eq. (23)

Here, w is a weighting factor. In some embodiments, w can be empiricallyset to 4. MV and MV^(s) indicate the current MV and the starting MV,respectively. SAD may still be used as the matching cost of templatematching at sub-CU level search.

In FRUC mode, MV is derived by using luma samples only. The derivedmotion will be used for both luma and chroma for MC inter prediction.After MV is decided, final MC is performed using 8-taps interpolationfilter for luma and 4-taps interpolation filter for chroma.

MV refinement is a pattern based MV search with the criterion ofbilateral matching cost or template matching cost. In the JEM, twosearch patterns are supported—an unrestricted center-biased diamondsearch (UCBDS) and an adaptive cross search for MV refinement at the CUlevel and sub-CU level, respectively. For both CU and sub-CU level MVrefinement, the MV is directly searched at quarter luma sample MVaccuracy, and this is followed by one-eighth luma sample MV refinement.The search range of MV refinement for the CU and sub-CU step are setequal to 8 luma samples.

In the bilateral matching merge mode, bi-prediction is applied becausethe motion information of a CU is derived based on the closest matchbetween two blocks along the motion trajectory of the current CU in twodifferent reference pictures. In the template matching merge mode, theencoder can choose among uni-prediction from list0, uni-prediction fromlist1, or bi-prediction for a CU. The selection ca be based on atemplate matching cost as follows:

If costBi <= factor * min (cost0, cost1)   bi-prediction is used; Otherwise, if cost0 <= cost1   uni-prediction from list0 is used; Otherwise,   uni-prediction from list1 is used;

Here, cost0 is the SAD of list0 template matching, cost1 is the SAD oflist1 template matching and costBi is the SAD of bi-prediction templatematching. For example, when the value of factor is equal to 1.25, itmeans that the selection process is biased toward bi-prediction. Theinter prediction direction selection can be applied to the CU-leveltemplate matching process.

2.8 Examples of Bi-Directional Optical Flow (BIO)

The bi-directional optical flow (BIO) method is a sample-wise motionrefinement performed on top of block-wise motion compensation forbi-prediction. In some implementations, the sample-level motionrefinement does not use signaling.

Let I^((k)) be the luma value from reference k (k=0, 1) after blockmotion compensation, and denote ∂I^((k))/∂x and ∂I^((k))/∂y as thehorizontal and vertical components of the I^((k)) gradient,respectively. Assuming the optical flow is valid, the motion vectorfield (v_(x), v_(y)) is given by:

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  Eq. (24)

Combining this optical flow equation with Hermite interpolation for themotion trajectory of each sample results in a unique third-orderpolynomial that matches both the function values I^((k)) and derivatives∂I^((k))/∂x and ∂I^((k))/∂y at the ends. The value of this polynomial att=0 is the BIO prediction:

pred_(BIO)=½·(I ⁽⁰⁾ +I ⁽¹⁾ +v _(x)/2·(τ₁ ∂I ⁽¹⁾ /∂x−τ ₀ I ⁽⁰⁾ /∂x)+v_(y)/2·(τ₁ I ⁽¹⁾ /∂y−τ ₀ ∂I ⁽⁰⁾ /∂y)).  Eq. (25)

FIG. 23 shows an example optical flow trajectory in the Bi-directionalOptical flow (BIO) method. Here, τ₀ and τ₁ denote the distances to thereference frames. Distances τ₀ and τ₁ are calculated based on POC forRef₀ and Ref₁: τ₀=POC(current)−POC(Ref₀), τ₁=POC(Ref₁)−POC(current). Ifboth predictions come from the same time direction (either both from thepast or both from the future) then the signs are different (e.g.,τ₀·τ₁<0). In this case, BIO is applied if the prediction is not from thesame time moment (e.g., τ₀≠σ₁). Both referenced regions have non-zeromotion (e.g., MVx₀, MVy₀, MVx₁, MVy₁≠0) and the block motion vectors areproportional to the time distance (e.g., MVx₀/MVx₁=MVy₀/MVy₁=−τ₀/τ₁)

The motion vector field (v_(x), v_(y)) is determined by minimizing thedifference Δ between values in points A and B. FIGS. 9A-9B show anexample of intersection of motion trajectory and reference frame planes.Model uses only first linear term of a local Taylor expansion for Δ:

Δ=(I ⁽⁰⁾ −I ⁽¹⁾ ₀ +v _(x)(τ₁∂⁽¹⁾ /∂x+τ ₀ ∂I ⁽⁰⁾ /∂x)+v _(y)(τ₁ ∂I ⁽¹⁾/∂y+τ ₀ ∂I ⁽⁰⁾ /∂y))  Eq. (26)

All values in the above equation depend on the sample location, denotedas (i′,j′). Assuming the motion is consistent in the local surroundingarea, A can be minimized inside the (2M+1)×(2M+1) square window Ωcentered on the currently predicted point (i,j), where M is equal to 2:

$\begin{matrix}{\left( {v_{x},v_{y}} \right) = {\underset{v_{x},v_{y}}{argmin}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\Delta^{2}\left\lbrack {i^{\prime},j^{\prime}} \right\rbrack}}}} & {{Eq}.\mspace{14mu} (27)}\end{matrix}$

For this optimization problem, the JEM uses a simplified approach makingfirst a minimization in the vertical direction and then in thehorizontal direction. This results in the following:

$\begin{matrix}{\mspace{79mu} {v_{x} = {\left( {s_{1} + r} \right) > {{m?\mspace{14mu} {clip}}\; 3\left( {{- {thBIO}},{thBIO},{- \frac{s_{3}}{\left( {s_{1} + r} \right)}}} \right)\text{:}0}}}} & {{Eq}.\mspace{14mu} (28)} \\{{v_{y} = {\left( {s_{5} + r} \right) > {{m?\mspace{14mu} {clip}}\; 3\left( {{- {thBIO}},{thBIO},{- \frac{s_{6} - {v_{x}{s_{2}/2}}}{\left( {s_{5} + r} \right)}}} \right)\text{:}0}}}\mspace{20mu} {{where},}} & {{Eq}.\mspace{14mu} (29)} \\{\mspace{79mu} {{{s_{1} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)^{2}}};}\mspace{20mu} {{s_{3} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {I^{(1)} - I^{(0)}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)}}};}{{s_{2} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)}}};}\mspace{20mu} {{s_{5} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)^{2}}};}\mspace{20mu} {s_{6} = {\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {I^{(1)} - I^{(0)}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)}}}}} & {{Eq}.\mspace{14mu} (30)}\end{matrix}$

In order to avoid division by zero or a very small value, regularizationparameters r and m can be introduced in Eq. (28) and Eq. (29), where:

r=500·4^(d-8)  Eq. (31)

m=700·4^(d-8)  Eq. (32)

Here, d is bit depth of the video samples.

In order to keep the memory access for BIO the same as for regularbi-predictive motion compensation, all prediction and gradients values,I^((k)), ∂I^((k))/∂x, ∂I^((k))/∂y are calculated for positions insidethe current block. FIG. 24A shows an example of access positions outsideof a block 2300. As shown in FIG. 24A, in Eq. (28), (2M+1)×(2M+1) squarewindow Ω centered in currently predicted point on a boundary ofpredicted block needs to accesses positions outside of the block. In theJEM, values of I^((k)), ∂I^((k))/θx, ∂I^((k))/∂y outside of the blockare set to be equal to the nearest available value inside the block. Forexample, this can be implemented as a padding area 2301, as shown inFIG. 24B.

With BIO, it is possible that the motion field can be refined for eachsample. To reduce the computational complexity, a block-based design ofBIO is used in the JEM. The motion refinement can be calculated based ona 4×4 block. In the block-based BIO, the values of s_(n) in Eq. (28) ofall samples in a 4×4 block can be aggregated, and then the aggregatedvalues of s_(n) in are used to derived BIO motion vectors offset for the4×4 block. More specifically, the following formula can used forblock-based BIO derivation:

$\begin{matrix}{\mspace{20mu} {{{s_{1,b_{k}} = {\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in {\Omega {({x,y})}}}\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)^{2}}}};}{{s_{3,b_{k}} = {\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {I^{(1)} - I^{(0)}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)}}}};}{{s_{2,b_{k}} = {\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial x}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial x}}}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)}}}};}\mspace{20mu} {{s_{5,b_{k}} = {\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)^{2}}}};}{s_{6,b_{k}} = {\sum\limits_{{({x,y})} \in b_{k}}{\sum\limits_{{\lbrack{i^{\prime},j}\rbrack} \in \Omega}{\left( {I^{(1)} - I^{(0)}} \right)\left( {{\tau_{1}{{\partial I^{(1)}}/{\partial y}}} + {\tau_{0}{{\partial I^{(0)}}/{\partial y}}}} \right)}}}}}} & {{Eq}.\mspace{14mu} (33)}\end{matrix}$

Here, b_(k) denotes the set of samples belonging to the k-th 4×4 blockof the predicted block. s_(n) in Eq (28) and Eq (29) are replaced by((s_(n,bk))>>4) to derive the associated motion vector offsets.

In some scenarios, MV regiment of BIO may be unreliable due to noise orirregular motion. Therefore, in BIO, the magnitude of MV regiment isclipped to a threshold value. The threshold value is determined based onwhether the reference pictures of the current picture are all from onedirection. For example, if all the reference pictures of the currentpicture are from one direction, the value of the threshold is set to12×2^(14-d); otherwise, it is set to 12×2^(13-d).

Gradients for BIO can be calculated at the same time with motioncompensation interpolation using operations consistent with HEVC motioncompensation process (e.g., 2D separable Finite Impulse Response (FIR)).In some embodiments, the input for the 2D separable FIR is the samereference frame sample as for motion compensation process and fractionalposition (fracX, fracY) according to the fractional part of block motionvector. For horizontal gradient ∂I/∂x, a signal is first interpolatedvertically using BIOfilterS corresponding to the fractional positionfracY with de-scaling shift d−8. Gradient filter BIOfilterG is thenapplied in horizontal direction corresponding to the fractional positionfracX with de-scaling shift by 18-d. For vertical gradient ∂I/∂y, agradient filter is applied vertically using BIOfilterG corresponding tothe fractional positionfracY with de-scaling shift d−8. The signaldisplacement is then performed using BIOfilterS in horizontal directioncorresponding to the fractional position fracX with de-scaling shift by18−d. The length of interpolation filter for gradients calculationBIOfilterG and signal displacement BIOfilterF can be shorter (e.g.,6-tap) in order to maintain reasonable complexity. Table 1 shows examplefilters that can be used for gradients calculation of differentfractional positions of block motion vector in BIO. Table 2 showsexample interpolation filters that can be used for prediction signalgeneration in BIO.

TABLE 1 Exemplary filters for gradient calculations in BIO FractionalInterpolation filter for gradient pel position (BIOfilterG) 0 { 8, −39,−3, 46, −17, 5} 1/16 { 8, −32, −13, 50, −18, 5} 1/8 { 7, −27, −20, 54,−19, 5} 3/16 { 6, −21, −29, 57, −18, 5} 1/4 { 4, −17, −36, 60, −15, 4}5/16 { 3, −9, −44, 61, −15, 4} 3/8 { 1, −4, −48, 61, −13, 3} 7/16 { 0,1, −54, 60, −9, 2} 1/2 { −1, 4, −57, 57, −4, 1}

TABLE 2 Exemplary interpolation filters for prediction signal generationin BIO Fractional Interpolation filter for prediction pel positionsignal(BIOfilterS) 0 { 0, 0, 64, 0, 0, 0} 1/16 { 1, −3, 64, 4, −2, 0}1/8 { 1, −6, 62, 9, −3, 1} 3/16 { 2, −8, 60, 14, −5, 1} 1/4 { 2, −9, 57,19, −7, 2} 5/16 { 3, −10, 53, 24, −8, 2} 3/8 { 3, −11, 50, 29, −9, 2}7/16 { 3, −11, 44, 35, −10, 3} 1/2 { 3, −10, 35, 44, −11, 3}

In the JEM, BIG can be applied to all bi-predicted blocks when the twopredictions are from different reference pictures. When LocalIllumination Compensation (LIC) is enabled for a CU, BIG can bedisabled.

In some embodiments, OBMC is applied for a block after normal MCprocess. To reduce the computational complexity, BIG may not be appliedduring the OBMC process. This means that BIG is applied in the MCprocess for a block when using its own MV and is not applied in the MCprocess when the MV of a neighboring block is used during the GOBMCprocess.

2.9 Examples of Decoder-Side Motion Vector Refinement (DMVR)

In a bi-prediction operation, for the prediction of one block region,two prediction blocks, formed using a motion vector (MV) of list0 and aMV of list1, respectively, are combined to form a single predictionsignal. In the decoder-side motion vector refinement (DMVR) method, thetwo motion vectors of the bi-prediction are further refined by abilateral template matching process. The bilateral template matchingapplied in the decoder to perform a distortion-based search between abilateral template and the reconstruction samples in the referencepictures in order to obtain a refined MV without transmission ofadditional motion information.

In DMVR, a bilateral template is generated as the weighted combination(i.e. average) of the two prediction blocks, from the initial MV0 oflist0 and MV1 of list1, respectively, as shown in FIG. 25. The templatematching operation consists of calculating cost measures between thegenerated template and the sample region (around the initial predictionblock) in the reference picture. For each of the two reference pictures,the MV that yields the minimum template cost is considered as theupdated MV of that list to replace the original one. In the JEM, nine MVcandidates are searched for each list. The nine MV candidates includethe original MV and 8 surrounding MVs with one luma sample offset to theoriginal MV in either the horizontal or vertical direction, or both.Finally, the two new MVs, i.e., MV0′ and MV1′ as shown in FIG. 25, areused for generating the final bi-prediction results. A sum of absolutedifferences (SAD) is used as the cost measure.

DMVR is applied for the merge mode of bi-prediction with one MV from areference picture in the past and another from a reference picture inthe future, without the transmission of additional syntax elements. Inthe JEM, when LIC, affine motion, FRUC, or sub-CU merge candidate isenabled for a CU, DMVR is not applied.

2.10 Examples of Symmetric Motion Vector Difference

Symmetric motion vector difference (SMVD) is proposed to encode the MVDmore efficiently.

Firstly, in slice level, variables BiDirPredFlag, RefIdxSymL0 andRefIdxSymL1 are derived as follows:

The forward reference picture in reference picture list 0 which isnearest to the current picture is searched. If found, RefIdxSymL0 is setequal to the reference index of the forward picture.

The backward reference picture in reference picture list 1 which isnearest to the current picture is searched. If found, RefIdxSymL1 is setequal to the reference index of the backward picture.

If both forward and backward picture are found, BiDirPredFlag is setequal to 1.

Otherwise, following applies:

The backward reference picture in reference picture list 0 which isnearest to the current one is searched. If found, RefIdxSymL0 is setequal to the reference index of the backward picture.

The forward reference picture in reference picture list 1 which isnearest to the current one is searched. If found, RefIdxSymL1 is setequal to the reference index of the forward picture.

If both backward and forward picture are found, BiDirPredFlag is setequal to 1. Otherwise, BiDirPredFlag is set equal to 0.

Secondly, in CU level, a symmetrical mode flag indicating whethersymmetrical mode is used or not is explicitly signaled if the predictiondirection for the CU is bi-prediction and BiDirPredFlag is equal to 1.

When the flag is true, only mvp_l0_flag, mvp_l1_flag and MVD0 areexplicitly signaled. The reference indices are set equal to RefIdxSymL0,RefIdxSymL1 for list 0 and list 1, respectively. MVD1 is just set equalto −MVD0. The final motion vectors are shown in below formula.

$\quad\left\{ \begin{matrix}{\left( {{mvx}_{0},{mvy}_{0}} \right) = \left( {{{mvpx}_{0} + {mvdx}_{0}},{{mvpy}_{0} + {mvdy}_{0}}} \right)} \\{\left( {{mvx}_{1},{mvy}_{1}} \right) = \left( {{{mvpx}_{1} - {mvdx}_{0}},{{mvpy}_{1} - {mvdy}_{0}}} \right)}\end{matrix} \right.$

FIG. 28 shows examples of symmetrical mode.

The modifications in coding unit syntax are shown in Table 3.

TABLE 3 Modifications in coding unit syntax Descriptor coding_unit( x0,y0, cbWidth, cbHeight, treeType ) { . . .    if( slice_type = = B )    inter_pred_idc[ x0 ][ y0 ] ae(v)    if( sps_affine_enabled_flag &&cbWidth >= 16 && cbHeight >= 16 ) {     inter_affine_flag[ x0 ][ y0 ]ae(v)     if( sps_affine_type_flag && inter_affine_flag[ x0 ][ y0 ] )     cu_affine_type_flag[ x0 ][ y0 ] ae(v)    }    if( inter_pred_idc[x0 ][ y0 ] == PRED_BI &&     BiDirPredFlag && inter_affine_flag[ x0 ][y0 ] == 0 )     symmetric_mvd_flag[ x0 ][ y0 ] ae(v)    if(inter_pred_idc[ x0 ][ y0 ] != PRED_L1 ) {     if(num_ref_idx_l0_active_minus1 > 0 && !symmetric_mvd_flag[ x0 ][ y0 ] )     ref_idx_l0[ x0 ][ y0 ] ae(v)     mvd_coding( x0, y0, 0, 0 )     if(MotionModelIdc[ x0 ][ y0 ] > 0 )      mvd_coding( x0, y0, 0, 1 )    if(MotionModelIdc[ x0 ][ y0 ] > 1 )      mvd_coding( x0, y0, 0, 2 )    mvp_l0_flag[ x0 ][ y0 ] ae(v)    } else {     MvdL0[ x0 ][ y0 ][ 0 ]= 0     MvdL0[ x0 ][ y0 ]] 1 ] = 0    }    if( inter_pred_idc[ x0 ][ y0] != PRED_L0 ) {     if( num_ref_idx_l1_active_minus1 > 0 &&!symmetric_mvd_flag[ x0 ][ y0 ] )      ref_idx_l1[ x0 ][ y0 ] ae(v)    if( mvd_l1_zero_flag && inter_pred_idc[ x0 ][ y0 ] = = PRED_BI ) {     . . .     } else {      if( !symmetric_mvd_flag[ x0 ][ y0 ] ) {      mvd_coding( x0, y0, 1, 0 )      if( MotionModelIdc[ x0][ y0 ] > 0)       mvd_coding( x0, y0, 1, 1 )      if(MotionModelIdc[ x0 ][ y0 ] >1 )       mvd_coding( x0, y0, 1, 2 )     }     mvp_l1_flag[ x0 ][ y0 ]ae(v)    } else {     MvdL1[ x0 ][ y0 ][ 0 ] = 0     MvdL1[ x0 ][ y0 ][1 ] = 0    }    . . .   }  }  . . . }

2.10.1 Symmetric MVD for Affine Bi-prediction Coding

SMVD for affine mode is proposed to extend the application of thesymmetric MVD mode to affine bi-prediction. When applying symmetric MVDmode to affine bi-prediction coding, the control point MVDs are notsignalled but derived. The top-left control point's MVD for the list-1is derived from list-0 based on the assumption of linear motion. Theother control point MVDs for list-0 are set to zero.

2.11 Context-Adaptive Binary Arithmetic Coding (CABAC)

2.11.1 CABAC Design in HEVC

2.11.1.1 Context Representation and Initialization Process in HEVC

In HEVC, for each context variable, the two variables pStateIdx andvalMps are initialized.

From the 8 bit table entry initValue, the two 4 bit variables slopeIdxand offsetIdx are derived as follows:

slopeIdx=initValue>>4

offsetIdx=initValue&15  (34)

The variables m and n, used in the initialization of context variables,are derived from slopeIdx and offsetIdx as follows:

m=slopeIdx*5−45

n=(offsetIdx>>3)−16  (35)

The two values assigned to pStateIdx and valMps for the initializationare derived from the luma's quantization parameter of slice denoted bySliceQpY. Given the variables m and n, the initialization is specifiedas follows:

preCtxState=Clip3(1,126,((m*Clip3(0,51,SliceQpY))>>4)+n)

valMps=(preCtxState<=63)?0:1

pStateIdx=valMps?(preCtxState−64):(63−preCtxState)  (36)

2.11.1.2 State transition process in HEVC

Inputs to this process are the current pStateIdx, the decoded valuebinVal and valMps values of the context variable associated withctxTable and ctxIdx.

Outputs of this process are the updated pStateIdx and valMps of thecontext variable associated with ctxIdx.

Depending on the decoded value binVal, the update of the two variablespStateIdx and valMps associated with ctxIdx is derived as follows in(37):

if( binVal = = valMps )  pStateIdx = transIdxMps( pStateIdx ) else { if( pStateIdx = = 0 ) valMps = 1 − valMps  pStateIdx = transIdxLps(pStateIdx ) }

2.11.2 CABAC design in VVC

The context-adaptive binary arithmetic coder (BAC) in VVC has beenchanged in VVC which is different from that in HEVC in terms of bothcontext updating process and arithmetic coder.

Here is the summary of recently adopted proposal (JVET-M0473, CE test5.1.13).

TABLE 4 Summary of CABAC modifications in VVC State 10 + 14 bit linear,reduced range representation rLPS 5 × 4 bit multiplier computationInitialization 128 × 16 bit to map HEVC-like state to linearrepresentation, retrained initialization values Rate estimation 256 × 2× 19 bit table Window size Variable, defined per context a = 2..5 b =a + 3..6 (controlling That is, each context has two variablesprobability for recording the associated probabilities, and updatingeach probability is updated with its own speed speed) (faster speedbased on the variable a and lower speed based on the variable b) OtherrMPS >= 128 is guaranteed

2.11.2.1 Context Initialization Process in VVC

In VVC, two values assigned to pStateIdx0 and pStateIdx1 for theinitialization are derived from SliceQpY. Given the variables m and n,the initialization is specified as follows:

preCtxState=Clip3(0,127,((m*Clip3(0,51,SliceQpY))>>4)+n)

pStateIdx0=initStateIdxToState[preCtxState]>>4

pStateIdx1=initStateIdxToState[preCtxState]  (38)

2.11.2.2 State Transition Process in VVC

Inputs to this process are the current pStateIdx0 and pStateIdx1, andthe decoded value binVal.

Outputs of this process are the updated pStateIdx0 and pStateIdx1 of thecontext variable associated with ctxIdx.

The variables shift0 (corresponding to variable a in Summary of CABACmodifications in VVCTable 4) and shift1 (corresponding to variable b inSummary of CABAC modifications in VVC Table 4) are derived from theshiftIdx value associated with ctxTable and ctxInc.

shift0=(shiftIdx>>2)+2

shift1=(shiftIdx&3)+3+shift0  (39)

Depending on the decoded value binVal, the update of the two variablespStateIdx0 and pStateIdx1 associated with ctxIdx is derived as follows:

pStateIdx0=pStateIdx0−(pStateIdx0>>shift0)+(1023*binVal>>shift0)

pStateIdx1=pStateIdx1−(pStateIdx1>>shift1)+(16383*binVal>>shift1)  (40)

3. Drawbacks of Existing Implementations

In some existing implementations, when MV/MV difference (MVD) could beselected from a set of multiple MV/MVD precisions for affine codedblocks, it remains uncertain how more accurate motion vectors may beobtained.

In other existing implementations, the MV/MVD precision information alsoplays an important role in determination of the overall coding gain ofAMVR applied to affine mode, but achieving this goal remains uncertain.

4. Example Methods for MV Predictors for Affine Mode with AMVR

Embodiments of the presently disclosed technology overcome the drawbacksof existing implementations, thereby providing video coding with highercoding efficiencies. The derivation and signaling of motion vectorpredictors for affine mode with adaptive motion vector resolution(AMVR), based on the disclosed technology, may enhance both existing andfuture video coding standards, is elucidated in the following examplesdescribed for various implementations. The examples of the disclosedtechnology provided below explain general concepts, and are not meant tobe interpreted as limiting. In an example, unless explicitly indicatedto the contrary, the various features described in these examples may becombined.

In some embodiments, the following examples may be applied to affinemode or normal mode when AMVR is applied. These examples assume that aprecision Prec (i.e., MV is with 1/(2{circumflex over ( )}Prec)precision) is used for encoding MVD in AF_INTER mode or for encoding MVDin normal inter mode. A motion vector predictor (e.g., inherited from aneighboring block MV) and its precision are denoted byMVPred(MVPred_(X), MVPred_(Y)) and PredPrec, respectively.

Improvement of Affine Mode with AMVR Supported

-   -   1. The set of allowed MVD precisions may be different from        picture to picture, from slice to slice, or from block to block.        -   a. In one example, the set of allowed MVD precisions may            depend on coded information, such as block size, block            shape. etc. al.        -   b. A set of allowed MV precisions may be pre-defined, such            as { 1/16, ¼, 1}.        -   c. Indications of allowed MV precisions may be signaled in            SPS/PPS/VPS/sequence header/picture header/slice            header/group of CTUs, etc. al.        -   d. The signaling of selected MV precision from a set of            allowed MV precisions further depend on number of allowed MV            precisions for a block.    -   2. A syntax element is signaled to the decoder to indicate the        used MVD precision in affine inter mode.        -   a. In one example, only one single syntax element is used to            indicate the MVD precisions applied to the affine mode and            the AMVR mode.            -   i. In one example, same semantics are used, that is, the                same value of syntax element is mapped to the same MVD                precision for the AMVR and affine mode.            -   ii. Alternatively, the semantics of the single syntax                element is different for the AMVR mode and the affine                mode. That is, the same value of syntax element could be                mapped to different MVD precision for the AMVR and                affine mode.        -   b. In one example, when affine mode uses same set of MVD            precisions with AMVR (e.g., MVD precision set is {1, ¼,            4}-pel), the MVD precision syntax element in AMVR is reused            in affine mode, i.e., only one single syntax element is            used.            -   i. Alternatively, furthermore, when encoding/decoding                this syntax element in CABAC encoder/decoder, same or                different context models may be used for AMVR and affine                mode.            -   ii. Alternatively, furthermore, this syntax element may                have different semantics in AMVR and affine mode. For                example, the syntax element equal to 0, 1 and 2                indicates ¼-pel, 1-pel and 4-pel MV precision                respectively in AMVR, while in affine mode, the syntax                element equal to 0, 1 and 2 indicates ¼-pel, 1/16-pel                and 1-pel MV precision respectively.        -   c. In one example, when affine mode uses same number of MVD            precisions with AMVR but different sets of MVD precisions            (e.g., MVD precision set for AMVR is {1, ¼, 4}-pel while for            affine, it is { 1/16, ¼, 1}-pel), the MVD precision syntax            element in AMVR is reused in affine mode, i.e., only one            single syntax element is used.            -   i. Alternatively, furthermore, when encoding/decoding                this syntax element in CABAC encoder/decoder, same or                different context models may be used for AMVR and affine                mode.            -   ii. Alternatively, furthermore, this syntax element may                have different semantics in AMVR and affine mode.        -   d. In one example, affine mode uses less MVD precisions than            AMVR, the MVD precision syntax element in AMVR is reused in            affine mode. However, only a subset of the syntax element            values is valid for affine mode.            -   i. Alternatively, furthermore, when encoding/decoding                this syntax element in CABAC encoder/decoder, same or                different context models may be used for AMVR and affine                mode.            -   ii. Alternatively, furthermore, this syntax element may                have different semantics in AMVR and affine mode.        -   e. In one example, affine mode uses more MVD precisions than            AMVR, the MVD precision syntax element in AMVR is reused in            affine mode. However, such syntax element is extended to            allow more values in affine mode.            -   i. Alternatively, furthermore, when encoding/decoding                this syntax element in CABAC encoder/decoder, same or                different context models may be used for AMVR and affine                mode.            -   ii. Alternatively, furthermore, this syntax element may                have different semantics in AMVR and affine mode.        -   f. In one example, a new syntax element is used for coding            the MVD precision of affine mode, i.e., two different syntax            elements are used for coding the MVD precision of AMVR and            affine mode.        -   g. The syntax for indication of MVD precisions for the            affine mode may be signaled under one or all of the            following conditions are true:            -   i. MVDs for all control points are non-zero.            -   ii. MVDs for at least one control point is non-zero.            -   iii. MVD of one control point (e.g., the first CPMV) are                non-zero        -    In this case, when either one of the above conditions or            all of them fail, there is no need to signal the MVD            precisions.        -   h. The syntax element for indication of MVD precisions for            either affine mode or the AMVR mode may be coded with            contexts and the contexts are dependent on coded            information.            -   i. In one example, when there is only one single syntax                element, the contexts may depend on whether current                block is coded with affine mode or not.        -   i. In one example, the context may depend on the block            size/block shape/MVD precisions of neighboring            blocks/temporal layer index/prediction directions, etc. al.        -   j. Whether to enable or disable the usage of multiple MVD            precisions for the affine mode may be signaled in            SPS/PPS/VPS/sequence header/picture header/slice            header/group of CTUs, etc. al.            -   i. In one example, whether to signal the information of                enable or disable the usage of multiple MVD precisions                for the affine mode may depend on other syntax elements.                For example, the information of enable or disable the                usage of multiple MV and/or MVP and/or MVD precisions                for the affine mode is signaled when affine mode is                enabled; and is not signaled and inferred to be 0 when                affine mode is disabled.        -   k. Alternatively, multiple syntax elements may be signaled            to indicate the used MV and/or MVP and/or MVD precision (in            the following discussion, they are all referred to as “MVD            precision”) in affine inter mode.            -   i. In one example, the syntax elements used to indicate                the used MVD precision in affine inter mode and normal                inter mode may be different.                -   1. The number of syntax elements to indicate the                    used MVD precision in affine inter mode and normal                    inter mode may be different.                -   2. The semantics of the syntax elements to indicate                    the used MVD precision in affine inter mode and                    normal inter mode may be different.                -   3. The context models in arithmetic coding to code                    one syntax elements to indicate the used MVD                    precision in affine inter mode and normal inter mode                    may be different.                -   4. The methods to derive context models in                    arithmetic coding to code one syntax element to                    indicate the used MVD precision in affine inter mode                    and normal inter mode may be different.            -   ii. In one example, a first syntax element (e.g.                amvr_flag) may be signaled to indicate whether to apply                AMVR in an affine-coded block.                -   1. The first syntax element is conditionally                    signaled.                -    a. In one example, signalling of the first syntax                    element (amvr_flag) is skipped when current block is                    coded with certain mode (e.g., CPR/IBC mode).                -    b. In one example, signalling of the first syntax                    element (amvr_flag) is skipped when all CPMVs' MVDs                    (including both horizontal and vertical components)                    are all zero.                -    c. In one example, signalling of the first syntax                    element (amvr_flag) is skipped when one selected                    CPMVs' MVDs (including both horizontal and vertical                    components) are all zero.                -    i. In one example, the selected CPMV's MVD is the                    first CPMV's MVD to be coded/decoded.                -    d. In one example, signalling of the first syntax                    element (amvr_flag) is skipped when the usage of                    enabling multiple MVD precisions for affine-coded                    block is false.                -    e. In one example, the first syntax element may be                    signaled under the following conditions:                -    i. Usage of enabling multiple MVD precisions for                    affine-coded block is true and current block is                    coded with affine mode;                -    ii. Alternatively, usage of enabling multiple MVD                    precisions for affine-coded block is true, current                    block is coded with affine mode, and at least one                    component of a CPMV's MVD is unequal to 0. iii.                    Alternatively, usage of enabling multiple MVD                    precisions for affine-coded block is true, current                    block is coded with affine mode, and at least one                    component of a selected CPMV's MVD is unequal to 0.                -    1. In one example, the selected CPMV's MVD is the                    first CPMV's MVD to be coded/decoded.                -    2. When AMVR is not applied to an affine-coded                    block or the first syntax element is not present, a                    default MV and/or MVD precision is utilized.                -    a. In one example, the default precision is ¼-pel.                -    b. Alternatively, the default precision is set to                    that used in motion compensation for affine coded                    blocks.                -    3. For example, the MVD precision of affine mode is                    ¼-pel if amvr_flag is equal to 0; otherwise the MVD                    precision of affine mode may be other values.                -    a. Alternatively, furthermore, the additional MVD                    precisions may be further signaled via a second                    syntax element.            -   iii. In one example, a second syntax element (such as                amvr_coarse_precision_flag) may be signaled to indicate                the MVD precision of affine mode.                -   1. In one example, whether the second syntax element                    is signaled may depend on the first syntax element.                    For example, the second syntax element is only                    signaled when the first syntax element is 1.                -   2. In one example, the MVD precision of affine mode                    is 1-pel if the second syntax element is 0;                    otherwise, the MVD precision of affine mode is                    1/16-pel.                -   3. In one example, the MVD precision of affine mode                    is 1/16-pel if the second syntax element is 0;                    otherwise, the MVD precision of affine mode is                    full-pixel.            -   iv. In one example, a syntax element used to indicate                the used MVD precision in affine inter mode share the                same context models as the syntax element with the same                name but used to indicate the used MVD precision in                normal inter mode.                -   1. Alternatively, a syntax element used to indicate                    the used MVD precision in affine inter mode use                    different context models as the syntax element with                    the same name but used to indicate the used MVD                    precision in normal inter mode.    -   3. Whether to apply or how to apply AMVR on an affine coded        block may depend on the reference picture of the current        block. i. In one example, AMVR is not applied if the reference        picture is the current picture,    -    i.e., Intra block copying is applied in the current block.

Fast Algorithm of AVMR in Affine Mode for Encoder

Denote RD cost (real RD cost, or SATD/SSE/SAD cost plus rough bits cost)of affine mode and AMVP mode as affineCosti and amvpCosti for IMV=i,where in i=0, 1 or 2. Here, IMV=0 means ¼ pel MV, and IMV=1 meansinteger MV for AMVP mode and 1/16 pel MV for affine mode, and IMV=2means 4 pel MV for AMVP mode and integer MV for affine mode. Denote RDcost of merge mode as mergeCost.

-   -   4. It is proposed that AMVR is disabled for affine mode of        current CU if the best mode of its parent CU is not AF_INTER        mode or AF_MERGE mode.        -   a. Alternatively, AMVR is disabled for affine mode of            current CU if the best mode of its parent CU is not AF_INTER            mode    -   5. It is proposed that AMVR is disabled for affine mode if        affineCost0>th1*amvpCost0, wherein th1 is a positive threshold.        -   a. Alternatively, in addition, AMVR is disabled for affine            mode if min(affineCost0, amvpCost0)>th2*mergeCost, wherein            th2 is a positive threshold.        -   b. Alternatively, in addition, integer MV is disabled for            affine mode if affineCost0>th3*affineCost1, wherein th3 is a            positive threshold.    -   6. It is proposed that AMVR is disabled for AMVP mode if        amvpCost0>th4*affineCost0, wherein th4 is a positive threshold.        -   a. Alternatively, AMVR is disabled for AMVP mode if            min(affineCost0, amvpCost0)>th5*mergeCost, wherein th5 is a            positive threshold.    -   7. It is proposed that 4/6 parameter affine models obtained in        one MV precision may be used as a candidate start search point        for other MV precisions.        -   a. In one example, 4/6 parameter affine models obtained in            1/16 MV may be used as a candidate start search point for            other MV precisions.        -   b. In one example, 4/6 parameter affine models obtained in ¼            MV may be used as a candidate start search point for other            MV precisions.    -   8. AMVR for affine mode is not checked at encoder for the        current block if its parent block does not choose the affine        mode.    -   9. Statistics of usage of different MV precisions for        affine-coded blocks in previously coded frames/slices/tiles/CTU        rows may be utilized to early terminate the rate-distortion        calculations of MV precisions for affine-coded blocks in current        slice/tile/CTU row.        -   a. In one example, the percentage of affine-coded blocks            with a certain MV precision is recorded. If the percentage            is too low, then the checking of the corresponding MV            precision is skipped.        -   b. In one example, previously coded frames with the same            temporal layer are utilized to decide whether to skip a            certain MV precision.    -   10. The above proposed method may be applied under certain        conditions, such as block sizes, slice/picture/tile types, or        motion information.        -   a. In one example, when a block size contains smaller than            M*H samples, e.g., 16 or 32 or 64 luma samples, proposed            method is not allowed.        -   b. Alternatively, when minimum size of a block's width            or/and height is smaller than or no larger than X, proposed            method is not allowed. In one example, X is set to 8.        -   c. Alternatively, when minimum size of a block's width            or/and height is no smaller than X, proposed method is not            allowed. In one example, X is set to 8.        -   d. Alternatively, when a block's width>th1 or >=th1 and/or a            block's height>th2 or >=th2, proposed method is not allowed.            In one example, th1 and/or th2 is set to 8.        -   e. Alternatively, when a block's width<th1 or <=th1 and/or a            block's height<th2 or <=th2, proposed method is not allowed.            In one example, th1 and/or th2 is set to 8.        -   f. Alternatively, whether to enable or disable the above            methods and/or which method to be applied may be dependent            on block dimension, video processing data unit (VPDU),            picture type, low delay check flag, coded information of            current block (such as reference pictures, uni or            bi-prediction) or previously coded blocks.    -   11. The AMVR methods for affine mode may be performed in        different ways when intra block copy (IBC, a.k.a. current        picture reference (CPR)) is applied or not.        -   a. In one example, AMVR for affine mode cannot be used if a            block is coded by IBC.        -   b. In one example, AMVR for affine mode may be used if a            block is coded by IBC, but the candidate MV/MVD/MVP            precisions may be different to those used for non-IBC coded            affine-coded block.    -   12. All the term “slice” in the document may be replaced by        “tile group” or “tile”.    -   13. In VPS/SPS/PPS/slice header/tile group header, a syntax        element (e.g. no_amvr_constraint_flag) equal to 1 specifies that        it is a requirement of bitstream conformance that both the        syntax element to indicate whether AMVR is enabled (e.g.        sps_amvr_enabled_flag) and the syntax element to indicate        whether affine AMVR is enabled (e.g.        sps_affine_avmr_enabled_flag) shall be equal to 0. The syntax        element (e.g. no_amvr_constraint_flag) equal to 0 does not        impose a constraint.    -   14. In VPS/SPS/PPS/slice header/tile group header or other video        data units, a syntax element (e.g.        no_affine_amvr_constraint_flag) may be signalled.        -   a. In one example, no_affine_amvr_constraint_flag equal to 1            specifies that it is a requirement of bitstream conformance            that the syntax element to indicate whether affine AMVR is            enabled (e.g. sps_affine_avmr_enabled_flag) shall be equal            to 0. The syntax element (e.g.            no_affine_amvr_constraint_flag) equal to 0 does not impose a            constraint

1. EMBODIMENTS 1.1. Embodiment 1: Indication of Usage of Affine AMVRMode

It may be signaled in SPS/PPS/VPS/APS/sequence header/pictureheader/tile group header, etc. al. This section presents the signallingin SPS.

1.1.1. SPS Syntax Table

seq_parameter_set_rbsp( ) { Descriptor  sps_seq_parameter_set_id ue(v)...  sps_amvr_enabled_flag u(1)  sps_bdof_enabled_flag u(1) sps_affine_amvr_enabled_flag u(1)  sps_cclm_enabled_flag u(1) sps_mts_intra_enabled_flag u(1)  sps_mts_inter_enabled_flag u(1) sps_affine_enabled_flag u(1)  if( sps_affine_enabled_flag )  sps_affine_type_flag u(1)  sps_gbi_enabled_flag u(1) sps_cpr_enabled_flag u(1) ...  rbsp_trailing bits( ) }

An alternative SPS syntax table is given as follows:

seq_parameter_set_rbsp( ) { Descriptor   sps_seq_parameter_set_id ue(v)  sps_amvr_enabled_flag u(1)   sps_bdof_enabled_flag u(1)  sps_cclm_enabled_flag u(1)   sps_mts_intra_enabled_flag u(1)  sps_mts_inter_enabled_flag u(1)   sps_affine_enabled_flag u(1)   if(sps_affine_enabled_flag ){     sps_affine_type_flag u(1)   sps_affine_amvr_enabled_flag u(1)  }   sps_gbi_enabled_flag u(1)  sps_cpr_enabled_flag u(1)   sps_ciip_enabled_flag u(1)  sps_triangle_enabled_flag u(1)   sps_ladf_enabled_flag u(1) ...  rbsp_trailing_bits( ) }

Semantics:

sps_affine_amvr_enabled_flag equal to specifies that adaptive motionvector difference resolution is used in motion vector coding of affineinter mode. amvr_enabled_flag equal to specifies that adaptive motionvector difference resolution is not used in motion vector coding ofaffine inter mode.

1.2. Parsing Process of Affine AMVR Mode Information

Syntax of the affine AMVR mode information may reuse that for the AMVRmode information (applied to normal inter mode). Alternatively,different syntax elements may be utilized. Affine AMVR mode informationmay be conditionally signaled. Different embodiments below show someexamples of the conditions.

1.2.1. Embodiment #1: CU Syntax Table

coding_unit( x0, y0, cbWidth, cbHeight, treeType ) { Descriptor  if(tile_group_type != I ) {   if( treeType != DUAL_TREE_CHROMA )   cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 )   pred_mode_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ){ ...   }  } else if( treeType != DUAL_TREE_CHROMA ) { /* MODE_INTER */  if( cu_skip_flag [ x0 ][ y0 ] = = 0 )    merge_flag[ x0 ][ y0 ] ae(v)  if( merge_flag[ x0 ][ y0 ] ) {    merge_data( x0, y0, cbWidth,cbHeight )   } else {    if( tile_group_type = = B )     inter_pred_idc[x0 ][ y0 ] ae(v)    if( sps_affine_enabled_flag && cbWidth >= 16 &&cbHeight >= 16 ) {     inter_affine_flag[ x0 ][ y0 ] ae(v)     if(sps_affine_type_flag && inter_affine_flag[ x0 ][ y0 ] )      cu_affine_type_flag[ x0 ][ y0 ] ae(v)    }    if( inter_pred_idc[x0 ][ y0 ] != PRED_L1 ) {     if( num_ref_idx_l0_active_minus1 > 0 )      ref_idx_l0[ x0 ][ y0 ] ae(v)     mvd_coding( x0, y0, 0, 0 )    if( MotionModelIdc[ x0 ][ y0 ] > 0 )       mvd_coding( x0, y0, 0, 1)     if(MotionModelIdc[ x0 ][ y0 ] > 1 )       mvd_coding( x0, y0, 0, 2)     mvp_l0_flag[ x0 ][ y0 ] ae(v)    } else {     MvdL0[ x0 ][ y0 ][ 0] = 0     MvdL0[ x0 ][ y0 ][ 1 ] = 0    }    if( inter_pred_idc[ x0 ][y0 ] != PRED_L0 ) {     if( num_ref_idx_l1_active_minus1 > 0 )      ref_idx_l1[ x0 ][ y0 ] ae(v)     if( mvd_l1_zero_flag &&inter_pred_idc[ x0 ][ y0 ] = = PRED_BI ) {       MvdL1[ x0 ][ y0 ][ 0 ]= 0       MvdL1[ x0 ][ y0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 0 ]= 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1 ][ 1 ] = 0       MvdCpL1[ x0 ][y0 ][ 2 ][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 2 ][ 1 ] = 0     } else {      mvd_coding( x0, y0, 1, 0 )     if( MotionModelIdc[ x0 ][ y0 ] > 0)       mvd_coding( x0, y0, 1, 1 )     if(MotionModelIdc[ x0 ][ y0 ] > 1)       mvd_coding( x0, y0, 1, 2 )     mvp_l1_flag[ x0 ][ y0 ] ae(v)   } else {     MvdL1[ x0 ][ y0 ][ 0 ] = 0     MvdL1[ x0 ][ y0 ][ 1 ] =0    }    if( ( sps_amvr_enabled_flag && inter_affine_flag = = 0 &&    ( MvdL0[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL0[ x0 ][ y0 ][ 1 ] != 0 ∥     MvdL1[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL1[ x0 ][ y0 ][ 1 ] != 0 ∥     (sps_affine_amvr_enabled_flag && inter_affine_flag = = 1 &&     (MvdCpL0[ x0 ][ y0 ][ 0 ] [ 0 ] != 0 ∥ MvdCpL0[ x0 ][ y0 ][ 0 ] [ 1 ] !=0 ∥      MvdCpL1[ x0 ][ y0 ][ 0 ] [ 0 ] != 0 ∥ MvdCpL1[ x0 ][ y0 ][ 0 ][ 1 ] != 0 ∥      MvdCpL0[ x0 ][ y0 ][ 1 ] [ 0 ] != 0 ∥ MvdCpL0[ x0 ][y0 ][ 1 ] [ 1 ] != 0 ∥      MvdCpL1[ x0 ][ y0 ][ 1 ] [ 0 ] != 0 ∥MvdCpL1[ x0 ][ y0 ][ 1 ] [ 1 ] != 0 ∥      MvdCpL0[ x0 ][ y0 ][ 2 ] [ 0] != 0 ∥ MvdCpL0[ x0 ][ y0 ][ 2 ] [ 1 ] != 0 ∥      MvdCpL1[ x0 ][ y0 ][2 ] [ 0 ] != 0 ∥ MvdCpL1[ x0 ][ y0 ][ 2 ] [ 1 ] != 0 ) ) ) {     if(!sps_cpr_enabled_flag ∥ !( inter_pred_idc[ x0 ][ y0 ] = = PRED_L0 && ref_idx_l0[ x0 ][ y0 ] = = num_ref_idx_l0_active_minus1 ) )      amvr_flag[ x0 ][ y0 ] ae(v)     if( amvr_flag[ x0 ][ y0 ] )      amvr_coarse_precisoin_flag[ x0 ][ y0 ] ae(v)    }    if(sps_gbi_enabled_flag && inter_pred_idc[ x0 ][ y0 ] = = PRED_BI &&    cbWidth * cbHeight >= 256)     gbi_idx[ x0 ][ y0 ] ae(v)   }  }  if(!pcm_flag[ x0 ][ y0 ] ) {   if( CuPredMode[ x0 ][ y0 ] != MODE_INTRA &&cu_skip_flag[ x0 ][ y0 ] = = 0 )    cu_cbf ae(v)   if( cu_cbf )   transform_tree( x0, y0, cbWidth, cbHeight, treeType )  } }

1.2.2. Embodiment 2: An Alternative CU Syntax Table Design

coding_unit( x0, y0, cbWidth, cbHeight, treeType ) { Descriptor  if(tile_group_type != I ) {   if( treeType != DUAL_TREE_CHROMA )   cu_skip_flag[ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0 )   pred_mode_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE INTRA ){ ...   }  } else if( treeType != DUAL_TREE_CHROMA ) { /* MODE_INTER */  if( cu_skip_flag [ x0 ][ y0 ] = = 0 )    merge_flag[ x0 ][ y0 ] ae(v)  if( merge_flag[ x0 ][ y0 ] ) {    merge_data( x0, y0, cbWidth,cbHeight )   } else {    if( tile_group_type = = B )     inter_pred_idc[x0 ][ y0 ] ae(v)    if( sps_affine_enabled_flag && cbWidth >= 16 &&cbHeight >= 16 ) {     inter_affine_flag[ x0 ][ y0 ] ae(v)     if(sps_affine_type_flag && inter_affine_flag[ x0 ][ y0 ] )      cu_affine_type_flag[ x0 ][ y0 ] ae(v)    }    if( inter_pred_idc[x0 ][ y0 ] != PRED_L1 ) {     if( num_ref_idx_l0_active_minus1 > 0 )      ref_idx_l0[ x0 ][ y0 ] ae(v)     mvd_coding( x0, y0, 0, 0 )    if( MotionModelIdc[ x0 ][ y0 ] > 0 )       mvd_coding( x0, y0, 0, 1)     if(MotionModelIdc[ x0 ][ y0 ] > 1 )       mvd_coding( x0, y0, 0, 2)     mvp_l0_flag[ x0 ][ y0 ] ae(v)    } else {     MvdL0[ x0 ][ y0 ][ 0] = 0     MvdL0[ x0 ][ y0 ][ 1 ] = 0    }    if( inter_pred_idc[ x0 ][y0 ] != PRED_L0 ) {     if( num_ref_idx_l1_active_minus1 > 0 )      ref_idx_l1[ x0 ][ y0 ] ae(v)     if( mvd_l1_zero_flag &&inter_pred_idc[ x0 ][ y0 ] = = PRED_BI ) {       MvdL1[ x0 ][ y0 ][ 0 ]= 0       MvdL1[ x0 ][ y0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 0 ]= 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1 ][ 1 ] = 0       MvdCpL1[ x0 ][y0 ][ 2 ][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 2 ][ 1 ] = 0     } else {      mvd_coding( x0, y0, 1, 0 )     if( MotionModelIdc[ x0 ][ y0 ] > 0)       mvd_coding( x0, y0, 1, 1 )     if(MotionModelIdc[ x0 ][ y0 ] > 1)       mvd_coding( x0, y0, 1, 2 )     mvp_l1_flag[ x0 ][ y0 ] ae(v)   } else {     MvdL1[ x0 ][ y0 ][ 0 ] = 0     MvdL1[ x0 ][ y0 ][ 1 ] =0    }    if( ( sps_amvr_enabled_flag && inter_affine_flag = = 0 &&    ( MvdL0[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL0[ x0 ][ y0 ][ 1 ] != 0 ∥     MvdL1[ x0 ][ y0 ][ 0] != 0 ∥ MvdL1[ x0 ][ y0 ][ 1 ] != 0 ) ) ∥    ( sps_affine_amvr_enabled_flag && inter_affine_flag = = 1 &&     (MvdCpL0[ x0 ][ y0 ][ 0 ] [ 0 ] != 0 ∥ MvdCpL0[ x0 ][ y0 ][ 0 ] [ 1 ] !=0 ∥      MvdCpL1[ x0 ][ y0 ][ 0 ] [ 0 ] != 0 ∥ MvdCpL1[ x0 ][ y0 ][ 0 ][ 1 ] != 0 ) ) ) {     if( !sps_cpr_enabled_flag ∥ !( inter_pred_idc[ x0][ y0 ] = = PRED_L0 &&  ref_idx_l0[ x0 ][ y0 ] = =num_ref_idx_l0_active_minus1 ) )       amvr_flag[ x0 ][ y0 ] ae(v)    if( amvr_flag[ x0 ][ y0 ] )        amvr_coarse_precisoin_flag[ x0 ][y0 ] ae(v)    }    if( sps_gbi_enabled_flag && inter_pred_idc[ x0 ][ y0] = = PRED_BI &&     cbWidth * cbHeight >= 256 )     gbi_idx[ x0 ][ y0 ]ae(v)   }  }  if( !pcm_flag[ x0 ][ y0 ] ) {   if( CuPredMode[ x0 ][ y0 ]!= MODE_INTRA && cu_skip_flag[ x0 ][ y0 ] = = 0 )    cu_cbf ae(v)   if(cu_cbf )    transform_tree( x0, y0, cbWidth, cbHeight, treeType )  } }

1.2.3. Embodiment 3: A Third CU Syntax Table Design

coding_unit( x0, y0, cbWidth, cbHeight, treeType ) { Descriptor  if(tile_group_type != I ) {   if( treeType != DUAL_TREE_CHROMA )   cu_skip_flag [ x0 ][ y0 ] ae(v)   if( cu_skip_flag[ x0 ][ y0 ] = = 0)    pred_mode_flag ae(v)  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA) { ...   }  } else if( treeType != DUAL TREE CHROMA ) { /* MODE INTER*/   if( cu_skip_flag[ x0 ][ y0 ] = = 0 )    merge_flag[ x0 ][ y0 ]ae(v)   if( merge_flag[ x0 ][ y0 ] ) {    merge_data( x0, y0, cbWidth,cbHeight )   } else {    if( tile_group_type = =B )     inter_pred_idc[x0 ][ y0 ] ae(v)    if( sps_affine_enabled_flag && cbWidth >= 16 &&cbHeight >= 16 ) {     inter_affine_flag[ x0 ][ y0 ] ae(v)     if(sps_affine_type_flag && inter_affine_flag[ x0 ][ y0 ] )      cu_affine_type_flag[ x0 ][ y0 ] ae(v)    }    if( inter_pred_idc[x0 ][ y0 ] != PRED_L1 ) {     if( num_ref_idx_l0_active_minus1 > 0 )      ref_idx_l0[ x0 ][ y0 ] ae(v)     mvd_coding( x0, y0, 0, 0 )    if( MotionModelIdc[ x0 ][ y0 ] > 0 )       mvd_coding( x0, y0, 0, 1)     if( MotionModelIdc[ x0 ][ y0 ] > 1 )       mvd_coding( x0, y0, 0,2 )     mvp_l0_flag[ x0 ][ y0 ] ae(v)    } else {     MvdL0[ x0 ][ y0 ][0 ] = 0     MvdL0[ x0 ][ y0 ][ 1 ] = 0    }    if( inter_pred_idc[ x0 ][y0 ] != PRED_L0 ) {     if( num_ref_idx_l1_active_minus1 > 0 )      ref_id_l1[ x0 ][ y0 ] ae(v)     if( mvd_l1_zero_flag &&inter_pred_idc[ x0 ][ y0 ] = = PRED_BI ) {       MvdL1[ x0 ][ y0 ][ 0 ]= 0       MvdL1[ x0 ][ y0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 0 ]= 0       MvdCpL1[ x0 ][ y0 ][ 0 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1 ][ 1 ] = 0       MvdCpL1[ x0 ][y0 ][ 2 ][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 2 ][ 1 ] = 0     } else {      mvd_coding( x0, y0, 1, 0 )     if( MotionModelIc[ x0 ][ y0 ] > 0 )      mvd_coding( x0, y0, 1, 1 )     if( MotionModelIdc[ x0 ][ y0 ] > 1)       mvd_coding( x0, y0, 1, 2 )     mvp_l1_flag[ x0 ][ y0 ] ae(v)   } else {     MvdL1[ x0 ][ y0 ][ 0 ] = 0     MvdL1[ x0 ][ y0 ][ 1 ] =0    }    if( ( sps_amvr_enabled_flag && inter_affine_flag = = 0 &&    ( MvdL0[x0][y0][ 0 ] != 0 ∥ MvdL0[ x0 ][ y0 ][ 1 ] != 0 ∥     MvdL1[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL1[ x0 ][ y0 ][ 1 ] != 0 ) ) ∥    ( sps_affine_amvr_enabled_flag && inter_affine_flag = = 1) ) {    if( !sps_cpr_enabled_flag ∥ !( inter_pred_idc[ x0 ][ y0 ] = =PRED_L0 &&  ref_idx_l0[ x0 ][ y0 ] = = num_ref_idx_l0_active_minus1 ) )      amvr_flag[ x0 ][ y0 ] ae(v)     if( amvr_flag[ x0 ][ y0 ] )      amvr_coarse_precisoin_flag[ x0 ][ y0 ] ae(v)    }    if(sps_gbi_enabled_flag && inter_pred_idc[ x0 ][ y0 ] = = PRED_BI &&    cbWidth * cbHeight >= 256 )     gbi_idx[ x0 ][ y0 ] ae(v)   }  } if( !pcm_flag[ x0 ][ y0 ] ) {   if( CuPredMode[ x0 ][ y0 ] !=MODE_INTRA && cu_skip_flag[ x0 ][ y0 ] = = 0)    cu_cbf ae(v)   if(cu_cbf )    transform_tree( x0, y0, cbWidth, cbHeight, treeType )  } }

1.2.4. Embodiment 4: Syntax Table Design with Different Syntax for AMVRand Affine AMVR Mode

coding_unit( x0, y0, cbWidth, cbHeight, treeType ) {  if(tile_group_type != I ) {   if( treeType != DUAL_TREE_CHROMA )   cu_skip_flag[ x0 ][ y0 ]   if( cu_skip_flag[ x0 ][ y0 ] = = 0 )   pred_mode_flag  }  if( CuPredMode[ x0 ][ y0 ] = = MODE_INTRA ) { ...  }  } else if( treeType != DUAL_TREE_CHROMA ) { /*  MODE_INTER */   if(cu_skip_flag[ x0 ][ y0 ] = = 0 )    merge_flag[ x0 ][ y0 ]   if(merge_flag[ x0 ][ y0 ] ) {    merge_data( x0, y0, cbWidth, cbHeight )  } else {    if( tile_group_type = = B )     inter_pred_idc[ x0 ][ y0 ]   if( sps_affine_enabled_flag && cbWidth >= 16 && cbHeight >= 16 ) {    inter_affine_flag[ x0 ][ y0 ]     if( sps_affine_type_flag &&inter_affine_flag[ x0 ][ y0 ] )       cu_affine_type_flag[ x0 ][ y0 ]   }    if( inter_pred_idc[ x0 ][ y0 ] != PRED_L1 ) {     if(num_ref_idx_l0_active_minus1 > 0 )       ref_idx_l0[ x0 ][ y0 ]    mvd_coding( x0, y0, 0, 0 )     if( MotionModelIdc[ x0 ][ y0 ] > 0 )      mvd_coding( x0, y0, 0, 1 )     if(MotionModelIdc[ x0 ][ y0 ] > 1 )      mvd_coding( x0, y0, 0, 2 )     mvp_l0_flag[ x0 ][ y0 ]    } else {    MvdL0[ x0 ][ y0 ][ 0 ] = 0     MvdL0[ x0 ][ y0 ][ 1 ] = 0    }   if( inter_pred_idc[ x0 ][ y0 ] != PRED_L0 ) {     if(num_ref_idx_l1_active_minus1 > 0 )       ref_idx_l1[ x0 ][ y0 ]     if(mvd_l1_zero_flag && inter_pred_idc[ x0 ][ y0 ] = = PRED_BI ) {      MvdL1[ x0 ][ y0 ][ 0 ] = 0       MvdL1[ x0 ][ y0 ][ 1 ] = 0      MvdCpL1[ x0 ][ y0 ][ 0 ][ 0 ] = 0       MvdCpL1[ x0 ][ y0 ][ 0 ][1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 1 ][ 0 ] = 0       MvdCpL1[ x0 ][ y0][ 1 ][ 1 ] = 0       MvdCpL1[ x0 ][ y0 ][ 2 ][ 0 ] = 0       MvdCpL1[x0 ][ y0 ][ 2 ][ 1 ] = 0     } else {       mvd_coding( x0, y0, 1, 0 )    if( MotionModelIdc[ x0 ][ y0 ] > 0 )       mvd_coding( x0, y0, 1, 1)     if(MotionModelIdc[ x0 ][ y0 ] > 1 )       mvd_coding( x0, y0, 1, 2)     mvp_l1_flag[ x0 ][ y0 ]    } else {     MvdL1[ x0 ][ y0 ][ 0 ] = 0    MvdL1[ x0 ][ y0 ][ 1 ] = 0    }    if(sps_amvr_enabled_flag &&inter_affine_flag = = 0 &&     ( MvdL0[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL0[ x0][ y0 ][ 1 ] != 0 ∥      MvdL1[ x0 ][ y0 ][ 0 ] != 0 ∥ MvdL1[ x0 ][ y0][ 1 ] != 0 )) {     if( !sps_cpr_enabled_flag ∥ !( inter_pred_idc[ x0][ y0 ] = = PRED_L0 &&  ref_idx_l0[ x0 ][ y0 ] = =num_ref_idx_l0_active_minus1 ) )       amvr_flag[ x0 ][ y0 ]     if(amvr_flag[ x0 ][ y0 ] )       amvr_coarse_precisoin_flag[ x0 ][ y0 ]   } else if (conditionsA) {     if(conditionsB)       affine_amvr_flag[x0 ][ y0 ]     if( amvr_flag[ x0 ][ y0 ] )      affine_amvr_coarse_precisoin_flag[ x0 ][ y0 ]    }    if(sps_gbi_enabled_flag && inter_pred_idc[ x0 ][ y0 ] = = PRED_BI &&    cbWidth * cbHeight >= 256 )     gbi_idx[ x0 ][ y0 ]   }  }  if(!pcm_flag[ x0 ][ y0 ] ) {   if( CuPredMode[ x0 ][ y0 ] != MODE_INTRA &&cu_skip_flag[ x0 ][ y0 ] = = 0 )    cu_cbf   if( cu_cbf )   transform_tree( x0, y0, cbWidth, cbHeight, treeType )  } }

-   -   In one example, conditionsA is defined as follows:

(sps_affine_amvr_enabled_flag && inter_affine_flag==1 &&

-   -   (MvdCpL0[x0][y0][0][0]!=0∥

MvdCpL0[x0][y0][0][1]!=0

-   -   MvdCpL1[x0][y0][0][0]!=0∥

MvdCpL1[x0][y0][0][1]!=0∥

-   -   MvdCpL0[x0][y0][1][0]!=0 ∥

MvdCpL0[x0][y0][1][1]!=0∥

-   -   MvdCpL1[x0][y0][1][0]!=0 ∥

MvdCpL1[x0][y0][1][1]!=0∥

-   -   MvdCpL0[x0][y0][2][0]!=0 ∥

MvdCpL0[x0][y0][2][1]!=0 ∥

-   -   MvdCpL1[x0][y0][2][0]!=0 ∥

MvdCpL1[x0][y0][2][1]!=0))

Alternatively, conditionsA is defined as follows:

(sps_affine_amvr_enabled_flag && inter_affine_flag==1 &&

-   -   (MvdCpL0[x0][y0][0][0]!=0 ∥

MvdCpL0[x0][y0][0][1]!=0 ∥

-   -   MvdCpL1[x0][y0][0][0]!=0 ∥

MvdCpL1[x0][y0][0][1]!=0)

Alternatively, conditionsA is defined as follows:

(sps_affine_amvr_enabled_flag && inter_affine_flag==1 &&

-   -   (MvdCpLX[x0][y0][0][0]!=0 ∥

MvdCpLX[x0][y0][0][1]!=0)

wherein X is being 0 or 1.Alternatively, conditionsA is defined as follows:

(sps_affine_amvr_enabled_flag && inter_affine_flag==1)

-   -   In one example, conditionsB is defined as follows:

!sps_cpr_enabled_flag∥!(inter_pred_idc[x0][y0]==PRED_L0 &&

-   -   ref_idx_l0[x0][y0]==num_ref_idx_l0_active_minus1)        Alternatively, conditionsB is defined as follows:

!sps_cpr_enabled_flag II !(pred_mode[x0][y0]==CPR).

Alternatively, conditionsB is defined as follows:

!sps_ibc_enabled_flag II !(pred_mode[x0][y0]==IBC).

When different syntax elements are utilized to code AMVR or Affine AMVR,the context modeling and/or contexts used for the embodiments in 5.5which are applied to Affine AMVR may be applied accordingly.

1.2.5. Semantics

amvr_flag[x0][y0] specifies the resolution of motion vector difference.The array indices x0, y0 specify the location (x0, y0) of the top-leftluma sample of the considered coding block relative to the top-left lumasample of the picture. amvr_flag[x0][y0] equal to 0 specifies that theresolution of the motion vector difference is ¼ of a luma sample.amvr_flag[x0][y0] equal to 1 specifies that the resolution of the motionvector difference is further specified byamvr_coarse_precisoin_flag[x0][y0].

When amvr_flag[x0][y0] is not present, it is inferred as follows:

-   -   If sps_cpr_enabled_flag is equal to 1, amvr_flag[x0][y0] is        inferred to be equal to 1.    -   Otherwise (sps_cpr_enabled_flag is equal to 0),        amvr_flag[xA][y0] is inferred to be equal to 0.

amvr_coarse_precisoin_flag[x0][y0] equal to 1 specifies that theresolution of the motion vector difference is four luma samples wheninter_affine_flag is equal to 0, and 1 luma samples wheninter_affine_flag is equal to 1. The array indices x0, y0 specify thelocation (x0, y0) of the top-left luma sample of the considered codingblock relative to the top-left luma sample of the picture.

When amvr_coarse_precisoin_flag[x0][y0] is not present, it is inferredto be equal to 0.

If inter_affine_flag[x0][y0] is equal to 0, the variable MvShift is setequal to (amvr_flag[x0][y0]+amvr_coarse_precisoin_flag[x0][y0])<<1 andthe variables MvdL0[x0][y0][0], MvdL0[x0][y][1], MvdL1[x0][y0][0],MvdL1[x0][y0][1] are modified as follows:

MvdL0[x0][y0][0]=MvdL0[x0][y0][0]<<(MvShift+2)  (7-70)

MvdL0[x0][y0][1]=MvdL0[x0][y0][1]<<(MvShift+2)  (7-71)

MvdL1[x0][y0][0]=MvdL1[x0][y0][0]<<(MvShift+2)  (7-72)

MvdL1[x0][y0][1]=MvdL1[x0][y0][1]<<(MvShift+2)  (7-73)

If inter_affine_flag[x0][y0] is equal to 1, the variable MvShift is setequal to(amvr_coarse_precisoinag?(amvr_coarse_precisoin_flag<<1):(−(amvr_flag<<1)))and the variables MvdCpL0[x0][y0][0][0], MvdCpL0[x0][y0][0][1],MvdCpL0[x0][y0][1][0], MvdCpL0[x0][y0][1][1], MvdCpL0[x0][y0][2][0],MvdCpL0[x0][y0][2][1] are modified as follows:

MvdCpL0[x0][y0][0][0]=MvdCpL0[x0][y0][0][0]<<(MvShift+2)  (7-73)

MvdCpL1[x0][y0][0][1]=MvdCpL1[x0][y0][0][1]<<(MvShift+2)  (7-67)

MvdCpL0[x0][y0][1][0]=MvdCpL0[x0][y0][1][0]<<(MvShift+2)  (7-66)

MvdCpL1[x0][y0][1][1]=MvdCpL1[x0][y0][1][1]<<(MvShift+2)  (7-67)

MvdCpL0[x0][y0][2][0]=MvdCpL0[x0][y0][2][0]<<(MvShift+2)  (7-66)

MvdCpL1[x0][y0][2][1]=MvdCpL1[x0][y0][2][1]<<(MvShift+2)  (7-67)

Alternatively, if inter_affine_flag[x0][y0] is equal to 1, the variableMvShift is set equal to (affine_amvr_coarse_precisoin_flag ?(affine_amvr_coarse_precisoin_flag<<1): (−(affine_amvr_flag<<1))).

1.3. Rounding Process for Motion Vectors

The rounding process is modified that when the given rightShift value isequal to 0 (which happens for 1/16-pel precision), the rounding offsetis set to 0 instead of (1<<(rightShift−1)).

For example, the sub-clause of rounding process for MVs is modified asfollows:Inputs to this process are:

-   -   the motion vector mvX,    -   the right shift parameter rightShift for rounding,    -   the left shift parameter leftShift for resolution increase.        Output of this process is the rounded motion vector mvX.        For the rounding of mvX, the following applies:

offset=(rightShift==0)?0:(1<<(rightShift−1))  (8-371)

mvX[0](mvX[0]>=0?(mvX[0]+offset)>>rightShift:−((−mvX[0]+offset)>>rightShift))<<leftShift  (8-372)

mvX[1](mvX[1]>=0?(mvX[1]+offset)>>rightShift:−((−mvX[1]+offset)>>rightShift))<<leftShift  (8-373)

1.4. Decoding Process

The rounding process invoked in the affine motion vector derivationprocess are performed with the input of (MvShift+2) instead of beingfixed to be 2.

Derivation Process for Luma Affine Control Point Motion VectorPredictors

Inputs to this process are:

-   -   a luma location (xCb, yCb) of the top-left sample of the current        luma coding block relative to the top-left luma sample of the        current picture,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current luma coding block,    -   the reference index of the current coding unit refIdxLX, with X        being 0 or 1,    -   the number of control point motion vectors numCpMv.

Output of this process are the luma affine control point motion vectorpredictors mvpCpLX[cpIdx] with X being 0 or 1, and cpIdx=0 . . .numCpMv−1.

For the derivation of the control point motion vectors predictorcandidate list, cpMvpListLX with X being 0 or 1, the following orderedsteps apply:

The number of control point motion vector predictor candidates in thelist numCpMvpCandLX is set equal to 0.

The variables availableFlagA and availableFlagB are both set equal toFALSE.

. . .

The rounding process for motion vectors as specified in clause 8.4.2.14is invoked with mvX set equal to cpMvpLX[cpIdx], rightShift set equal to(MvShift+2), and leftShift set equal to (MvShift+2) as inputs and therounded cpMvpLX[cpIdx] with cpIdx=0 . . . numCpMv−1 as output.

. . .

The variable availableFlagA is set equal to TRUE

The derivation process for luma affine control point motion vectors froma neighbouring block as specified in clause 8.4.4.5 is invoked with theluma coding block location (xCb, yCb), the luma coding block width andheight (cbWidth, cbHeight), the neighbouring luma coding block location(xNb, yNb), the neighbouring luma coding block width and height (nbW,nbH), and the number of control point motion vectors numCpMv as input,the control point motion vector predictor candidates cpMvpLY[cpIdx] withcpIdx=0 . . . numCpMv−1 as output. The rounding process for motionvectors as specified in clause 8.4.2.14 is invoked with mvX set equal tocpMvpLY[cpIdx], rightShift set equal to (MvShift+2), and leftShift setequal to (MvShift+2) as inputs and the rounded cpMvpLY[cpIdx] withcpIdx=0 . . . numCpMv−1 as output.

. . .

The derivation process for luma affine control point motion vectors froma neighbouring block as specified in clause 8.4.4.5 is invoked with theluma coding block location (xCb, yCb), the luma coding block width andheight (cbWidth, cbHeight), the neighbouring luma coding block location(xNb, yNb), the neighbouring luma coding block width and height (nbW,nbH), and the number of control point motion vectors numCpMv as input,the control point motion vector predictor candidates cpMvpLX[cpIdx] withcpIdx=0 . . . numCpMv−1 as output.

The rounding process for motion vectors as specified in clause 8.4.2.14is invoked with mvX set equal to cpMvpLX[cpIdx], rightShift set equal to(MvShift+2), and leftShift set equal to (MvShift+2) as inputs and therounded cpMvpLX[cpIdx] with cpIdx=0 . . . numCpMv−1 as output.

The following assignments are made:

cpMvpListLX[numCpMvpCandLX][0]=cpMvpLX[0]  (8-618)

cpMvpListLX[numCpMvpCandLX][1]=cpMvpLX[1]  (8-619)

cpMvpListLX[numCpMvpCandLX][2]=cpMvpLX[2]  (8-620)

numCpMvpCandLX=numCpMvpCandLX+1  (8-621)

Otherwise if PredFlagLY[xNbBk][yNbBk] (with Y=!X) is equal to 1 andDiffPicOrderCnt(RefPicListY[RefIdxLY[xNbBk][yNbBk] ],RefPicListX[refIdxLX]) is equal to 0, the following applies:

The variable availableFlagB is set equal to TRUE

The derivation process for luma affine control point motion vectors froma neighbouring block as specified in clause 8.4.4.5 is invoked with theluma coding block location (xCb, yCb), the luma coding block width andheight (cbWidth, cbHeight), the neighbouring luma coding block location(xNb, yNb), the neighbouring luma coding block width and height (nbW,nbH), and the number of control point motion vectors numCpMv as input,the control point motion vector predictor candidates cpMvpLY[cpIdx] withcpIdx=0 . . . numCpMv−1 as output.

The rounding process for motion vectors as specified in clause 8.4.2.14is invoked with mvX set equal to cpMvpLY[cpIdx], rightShift set equal to(MvShift+2), and leftShift set equal to (MvShift+2) as inputs and therounded cpMvpLY[cpIdx] with cpIdx=0 . . . numCpMv−1 as output.

The following assignments are made:

cpMvpListLX[numCpMvpCandLX][0]=cpMvpLY[0]  (8-622)

cpMvpListLX[numCpMvpCandLX][1]=cpMvpLY[1]  (8-623)

cpMvpListLX[numCpMvpCandLX][2]=cpMvpLY[2]  (8-624)

numCpMvpCandLX=numCpMvpCandLX+1  (8-625)

When numCpMvpCandLX is less than 2, the following applies

The derivation process for constructed affine control point motionvector prediction candidate as specified in clause 8.4.4.8 is invokedwith the luma coding block location (xCb, yCb), the luma coding blockwidth cbWidth, the luma coding block height cbHeight, and the referenceindex of the current coding unit refIdxLX as inputs, and theavailability flag availableConsFlagLX, the availability flagsavailableFlagLX[cpIdx] and cpMvpLX[cpIdx] with cpIdx=0 . . . numCpMv−1as outputs.

When availableConsFlagLX is equal to 1, and numCpMvpCandLX is equal to0, the following assignments are made:

cpMvpListLX[numCpMvpCandLX][0]=cpMvpLX[0]  (8-626)

cpMvpListLX[numCpMvpCandLX][1]=cpMvpLX[1]  (8-627)

cpMvpListLX[numCpMvpCandLX][2]=cpMvpLX[2]  (8-628)

numCpMvpCandLX=numCpMvpCandLX+1  (8-629)

The following applies for cpIdx=0 . . . numCpMv−1:

When numCpMvpCandLX is less than 2 and availableFlagLX[cpIdx] is equalto 1, the following assignments are made:

cpMvpListLX[numCpMvpCandLX][0]=cpMvpLX[cpIdx]  (8-630)

cpMvpListLX[numCpMvpCandLX][1]=cpMvpLX[cpIdx]  (8-631)

cpMvpListLX[numCpMvpCandLX][2]=cpMvpLX[cpIdx]  (8-632)

numCpMvpCandLX=numCpMvpCandLX+1  (8-633)

When numCpMvpCandLX is less than 2, the following applies:

The derivation process for temporal luma motion vector prediction asspecified in clause 8.4.2.11 is with the luma coding block location(xCb, yCb), the luma coding block width cbWidth, the luma coding blockheight cbHeight and refIdxLX as inputs, and with the output being theavailability flag availableFlagLXCol and the temporal motion vectorpredictor mvLXCol.

When availableFlagLXCol is equal to 1, the following applies:

The rounding process for motion vectors as specified in clause 8.4.2.14is invoked the with mvX set equal to mvLXCol, rightShift set equal to(MvShift+2), and leftShift set equal to (MvShift+2) as inputs and therounded mvLXCol as output.

The following assignments are made:

cpMvpListLX[numCpMvpCandLX][0]=mvLXCol  (8-634)

cpMvpListLX[numCpMvpCandLX][1]=mvLXCol  (8-635)

cpMvpListLX[numCpMvpCandLX][2]=mvLXCol  (8-636)

numCpMvpCandLX=numCpMvpCandLX+1  (8-637)

When numCpMvpCandLX is less than 2, the following is repeated untilnumCpMvpCandLX is equal to 2, with mvZero[0] and mvZero[1] both beingequal to 0:

cpMvpListLX[numCpMvpCandLX][0]=mvZero  (8-638)

cpMvpListLX[numCpMvpCandLX][1]=mvZero  (8-639)

cpMvpListLX[numCpMvpCandLX][2]=mvZero  (8-640)

numCpMvpCandLX=numCpMvpCandLX+1  (8-641)

The affine control point motion vector predictor cpMvpLX with X being 0or 1 is derived as follows:

cpMvpLX=cpMvpListLX[mvp_lX_flag[xCb][yCb]]  (8-642)

Derivation Process for Constructed Affine Control Point Motion VectorPrediction Candidates

Inputs to this process are:

-   -   a luma location (xCb, yCb) specifying the top-left sample of the        current luma coding block relative to the top-left luma sample        of the current picture,    -   two variables cbWidth and cbHeight specifying the width and the        height of the current luma coding block,    -   the reference index of the current prediction unit partition        refIdxLX, with X being 0 or 1,

Output of this process are:

-   -   the availability flag of the constructed affine control point        motion vector prediction candidates availableConsFlagLX with X        being 0 or 1,    -   the availability flags availableFlagLX[cpIdx] with cpIdx=0 . . .        2 and X being 0 or 1,    -   the constructed affine control point motion vector prediction        candidates cpMvLX[cpIdx] with cpIdx=0 . . . numCpMv−1 and X        being 0 or 1.

The first (top-left) control point motion vector cpMvLX[0] and theavailability flag availableFlagLX[0] are derived in the followingordered steps:

The sample locations (xNbB2, yNbB2), (xNbB3, yNbB3) and (xNbA2, yNbA2)are set equal to (xCb−1, yCb−1), (xCb, yCb−1) and (xCb−1, yCb),respectively.

The availability flag availableFlagLX[0] is set equal to 0 and bothcomponents of cpMvLX[0] are set equal to 0.

The following applies for (xNbTL, yNbTL) withTL being replaced by B2,B3, and A2:

The availability derivation process for a coding block as specified inclause is invoked with the luma coding block location (xCb, yCb), theluma coding block width cbWidth, the luma coding block height cbHeight,the luma location (xNbY, yNbY) set equal to (xNbTL, yNbTL) as inputs,and the output is assigned to the coding block availability flagavailableTL.

When availableTL is equal to TRUE and availableFlagLX[0] is equal to 0,the following applies:

If PredFlagLX[xNbTL][yNbTL] is equal to 1, andDiffPicOrderCnt(RefPicListX[RefIdxLX[xNbTL][yNbTL] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLX[xNbTL][yNbTL] is not the current picture,availableFlagLX[0] is set equal to 1 and the following assignments aremade:

cpMvLX[0]=MvLX[xNbTL][yNbTL]  (8-643)

Otherwise, when PredFlagLY[xNbTL][yNbTL] (with Y=!X) is equal to 1 andDiffPicOrderCnt(RefPicListY[RefIdxLY[xNbTL][yNbTL] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLY[xNbTL][yNbTL] is not the current picture,availableFlagLX[0] is set equal to 1 and the following assignments aremade: cpMvLX[0]=MvLY[xNbTL][yNbTL] (8-644)

When availableFlagLX[0] is equal to 1, the rounding process for motionvectors as specified in clause 8.4.2.14 is invoked with mvX set equal tocpMvLX[0], rightShift set equal to (MvShift+2), and leftShift set equalto (MvShift+2) as inputs and the rounded cpMvLX[0] as output.

The second (top-right) control point motion vector cpMvLX[1] and theavailability flag availableFlagLX[1] are derived in the followingordered steps:

The sample locations (xNbB1, yNbB1) and (xNbB0, yNbB0) are set equal to(xCb+cbWidth−1, yCb−1) and (xCb+cbWidth, yCb−1), respectively.

The availability flag availableFlagLX[1] is set equal to 0 and bothcomponents of cpMvLX[1] are set equal to 0.

The following applies for (xNbTR, yNbTR) with TR being replaced by B1and B0:

The availability derivation process for a coding block as specified inclause 6.4.X is invoked with the luma coding block location (xCb, yCb),the luma coding block width cbWidth, the luma coding block heightcbHeight, the luma location (xNbY, yNbY) set equal to (xNbTR, yNbTR) asinputs, and the output is assigned to the coding block availability flagavailableTR.

When availableTR is equal to TRUE and availableFlagLX[1] is equal to 0,the following applies:

If PredFlagLX[xNbTR][yNbTR] is equal to 1, andDiffPicOrderCnt(RefPicListX[RefIdxLX[xNbTR][yNbTR] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLX[xNbTR][yNbTR] is not the current picture,availableFlagLX[1] is set equal to 1 and the following assignments aremade:

cpMvLX[1]=MvLX[xNbTR][yNbTR]  (8-645)

Otherwise, when PredFlagLY[xNbTR][yNbTR] (with Y=!X) is equal to 1 andDiffPicOrderCnt(RefPicListY[RefIdxLY[xNbTR][yNbTR] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLY[xNbTR][yNbTR] is not the current picture,availableFlagLX[1] is set equal to 1 and the following assignments aremade:

cpMvLX[1]=MvLY[xNbTR][yNbTR]  (8-646)

When availableFlagLX[1] is equal to 1, the rounding process for motionvectors as specified in clause 8.4.2.14 is invoked with mvX set equal tocpMvLX[1], rightShift set equal to (MvShift+2), and leftShift set equalto (MvShift+2) as inputs and the rounded cpMvLX[1] as output.

The third (bottom-left) control point motion vector cpMvLX[2] and theavailability flag availableFlagLX[2] are derived in the followingordered steps:

The sample locations (xNbA1, yNbA1) and (xNbA0, yNbA0) are set equal to(xCb−1, yCb+cbHeight−1) and (xCb−1, yCb+cbHeight), respectively.

The availability flag availableFlagLX[2] is set equal to 0 and bothcomponents of cpMvLX[2] are set equal to 0.

The following applies for (xNbBL, yNbBL) with BL being replaced by A1and A0:

The availability derivation process for a coding block as specified inclause 6.4.X invoked with the luma coding block location (xCb, yCb), theluma coding block width cbWidth, the luma coding block height cbHeight,the luma location (xNbY, yNbY) set equal to (xNbBL, yNbBL) as inputs,and the output is assigned to the coding block availability flagavailableBL.

When availableBL is equal to TRUE and availableFlagLX[2] is equal to 0,the following applies:

If PredFlagLX[xNbBL][yNbBL] is equal to 1, andDiffPicOrderCnt(RefPicListX[RefIdxLX[xNbBL][yNbBL] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLY[xNbBL][yNbBL] is not the current picture,availableFlagLX[2] is set equal to 1 and the following assignments aremade:

cpMvLX[2]=MvLX[xNbBL][yNbBL]  (8-647)

Otherwise, when PredFlagLY[xNbBL][yNbBL] (with Y=!X) is equal to 1 andDiffPicOrderCnt(RefPicListY[RefIdxLY[xNbBL][yNbBL] ],RefPicListX[refIdxLX]) is equal to 0, and the reference picturecorresponding to RefIdxLY[xNbBL][yNbBL] is not the current picture,availableFlagLX[2] is set equal to 1 and the following assignments aremade: cpMvLX[2]=MvLY[xNbBL][yNbBL] (8-648)

When availableFlagLX[2] is equal to 1, the rounding process for motionvectors as specified in clause 8.4.2.14 is invoked with mvX set equal tocpMvLX[2], rightShift set equal to (MvShift+2), and leftShift set equalto (MvShift+2) as inputs and the rounded cpMvLX[2] as output.

1.5. Context Modeling

Assignment of ctxInc to syntax elements with context coded bins:

binIdx Syntax element 0 1 2 3 4 >=5 amvr_flag[ ][ ] 0, 1, 2 na na na nana (clause 9.5.4.2.2, when inter_affine_flag[ ][ ] is equal to 0)amvr_coarse_precisoin_ 0 na na na na na flag[ ][ ]

Specification of ctxInc using left and above syntax elements:

In one example, context increasement offset ctxInc=(condL &&availableL)+(condA && availableA)+ctxSetIdx*3.

Alternatively, ctxInc=((condL && availableL) ∥ (condA &&availableA))+ctxSetIdx*3.

ctxInc=(condL&&availableL)+M*(condA&&availableA)+ctxSetIdx*3. (e.g.,M=2)

ctxInc=M*(condL&&availableL)+(condA&&availableA)+ctxSetIdx*3. (e.g.,M=2)

Syntax element condL condA ctxSetIdx e cu_skip_flag[ xNbL ]cu_skip_flag[ xNbA ] 0 [ yNbL ] [ yNbA ] e !inter_affine_flag[ x0 ]!inter_affine_flag[ x0 ] 0 [ y0 ] [ y0 ] && && amvr_flag[ xNbL ]amvr_flag[ xNbA ] [ yNbL ] [ yNbA ]

Values of initValue for ctxIdx of amvr_flag:

Different contexts are used when current block is affine or non-affine.

ctxIdx of amvr_flag Initialization ctxIdx of amvr_flag when wheninter_affine_flag is variable inter_affine_flag is equal to 0 equal to 1initValue 0 1 2 3 xx xx xx xx

Values of initValue for ctxIdx of amvr_coarse_precisoin_flag:

Different contexts are used when current block is affine or non-affine.

ctxIdx of amvr_coarse ctxIdx of Initiali- precisoin_flagamvr_coarse_precisoin_flag zation when inter_affine_flag when inter_variable is equal to 0 affine_flag is equal to 1 initValue 0 0 xxx xx

The examples described above may be incorporated in the context of themethod described below, e.g., methods 2600 to 2680, which may beimplemented at a video decoder or a video encoder.

FIG. 26A shows a flowchart of an exemplary method for video processing.The method 2600 includes, at step 2602, determining, for a conversionbetween a coded representation of a current block of a video and thecurrent block, a motion vector difference (MVD) precision to be used forthe conversion from a set of allowed multiple MVD precisions applicableto a video region containing the current video block. The method 2600includes, at step 2604, performing the conversion based on the MVDprecision.

FIG. 26B shows a flowchart of an exemplary method for video processing.The method 2610 as shown in FIG. 26B includes, at step 2612,determining, for a video region comprising one or more video blocks of avideo and a coded representation of the video, a usage of multiplemotion vector difference (MVD) precisions for the conversion of the oneor more video blocks in the video region. The method 2610 includes, atstep 2614, performing the conversion based on the determination.

FIG. 26C shows a flowchart of an exemplary method for video processing.The method 2620 as shown in FIG. 26C includes, at step 2622,determining, for a video region comprising one or more video blocks of avideo and a coded representation of the video, whether to apply anadaptive motion vector resolution (AMVR) process to a current videoblock for a conversion between the current video block and the codedrepresentation of the video. The method 2620 includes, at step 2624,performing the conversion based on the determining.

FIG. 26D shows a flowchart of an exemplary method for video processing.The method 2630 as shown in FIG. 26D includes, at step 2632,determining, for a video region comprising one or more video blocks of avideo and a coded representation of the video, how to apply an adaptivemotion vector resolution (AMVR) process to a current video block for aconversion between the current video block and the coded representationof the video. The method 2630 includes, at step 2634, performing theconversion based on the determining.

FIG. 26E shows a flowchart of an exemplary method for video processing.The method 2640 as shown in FIG. 26E includes, at step 2642,determining, based on a coding mode of a parent coding unit of a currentcoding unit that uses an affine coding mode or a rate-distortion (RD)cost of the affine coding mode, a usage of an adaptive motion vectorresolution (AMVR) for a conversion between a coded representation of acurrent block of a video and the current block. The method 2640includes, at step 2644, performing, the conversion according to a resultof the determining.

FIG. 26F shows a flowchart of an exemplary method for video processing.The method 2650 as shown in FIG. 26F includes, at step 2652, determininga usage of an adaptive motion vector resolution (AMVR) for a conversionbetween a coded representation of a current block of a video and thecurrent block that uses an advanced motion vector prediction (AMVP)coding mode, the determining based on a rate-distortion (RD) cost of theAMVP coding mode. The method 2650 includes, at step 2654, performing,the conversion according to a result of the determining.

FIG. 26G shows a flowchart of an exemplary method for video processing.The method 2660 as shown in FIG. 26G includes, at step 2662, generating,for a conversion between a coded representation of a current block of avideo and the current block, a set of MV (Motion Vector) precisionsusing a 4-parameter affine model or 6-parameter affine model. The method2660 includes, at step 2664, performing, the conversion based on the setof MV precisions.

FIG. 26H shows a flowchart of an exemplary method for video processing.The method 2670 as shown in FIG. 26H includes, at step 2672,determining, based on a coding mode of a parent block of a current blockthat uses an affine coding mode, whether an adaptive motion vectorresolution (AMVR) tool is used for a conversion, wherein the AMVR toolis used to refine motion vector resolution during decoding. The method2670 includes, at step 2674, performing the conversion according to aresult of the determining.

FIG. 26I shows a flowchart of an exemplary method for video processing.The method 2680 as shown in FIG. 26I includes, at step 2682,determining, based on a usage of MV precisions for previous blocks thathas been previously coded using an affine coding mode, a termination ofa rate-distortion (RD) calculations of MV precisions for a current blockthat uses the affine coding mode for a conversion between a codedrepresentation of the current block and the current block. The method2680 includes, at step 2684, performing the conversion according to aresult of the determining.

5. Example Implementations of the Disclosed Technology

FIG. 27 is an example of a block diagram of a video processing apparatus2700. The apparatus 2700 may be used to implement one or more of themethods described herein. The apparatus 2700 may be embodied in asmartphone, tablet, computer, Internet of Things (IoT) receiver, and soon. The apparatus 2700 may include one or more processors 2702, one ormore memories 2704 and video processing hardware 2706. The processor(s)2702 may be configured to implement one or more methods (including, butnot limited to, methods 2610 to 2680) described in the present document.The memory (memories) 2704 may be used for storing data and code usedfor implementing the methods and techniques described herein. The videoprocessing hardware 2706 may be used to implement, in hardwarecircuitry, some techniques described in the present document.

FIG. 29 is another example of a block diagram of a video processingsystem in which disclosed techniques may be implemented. FIG. 29 is ablock diagram showing an example video processing system 2900 in whichvarious techniques disclosed herein may be implemented. Variousimplementations may include some or all of the components of the system2900. The system 2900 may include input 2902 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 2902 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 2900 may include a coding component 2904 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 2904 may reduce the average bitrate ofvideo from the input 2902 to the output of the coding component 2904 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 2904 may be eitherstored, or transmitted via a communication connected, as represented bythe component 2906. The stored or communicated bitstream (or coded)representation of the video received at the input 2902 may be used bythe component 2908 for generating pixel values or displayable video thatis sent to a display interface 2910. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

In some embodiments, the video processing methods may be implementedusing an apparatus that is implemented on a hardware platform asdescribed with respect to FIG. 27 or 29.

Various techniques and embodiments may be described using the followingclause-based format. These clauses may be implemented as preferredfeatures of some embodiments.

The first set of clauses use some of the techniques described in theprevious section, including, for example, items 1, 2, and 13-15 in theprevious section.

1. A method of video processing, comprising: determining, for aconversion between a coded representation of a current block of a videoand the current block, a motion vector difference (MVD) precision to beused for the conversion from a set of allowed multiple MVD precisionsapplicable to a video region containing the current video block; andperforming the conversion based on the MVD precision.

2. The method of clause 1, wherein the set of allowed multiple MVDprecisions depends on a picture, a slice, or a block of the video data.

3. The method of clause 1, wherein the set of allowed multiple MVDprecisions depends on coded information of the current block.

4. The method of clause 1, wherein the set of allowed multiple MVDprecisions is pre-defined.

5. The method of clause 1, wherein the set of allowed multiple MVDprecisions is signaled in a Sequence Parameter Set (SPS), a PictureParameter Set (PPS), a Video Parameter Set (VPS), a sequence header, apicture header, a slice header, a group of coding tree unit s (CTUs).

6. The method of clause 1, further comprising signaling a determined MVDprecision from the set of allowed multiple MVD precision based on anumber of allowed MV precisions for the current block.

7. The method of clause 1, wherein the determining of the MVD precisionis based on one or more syntax elements, and wherein the current blockis coded using an affine mode.

8. The method of clause 3 or 7, wherein same syntax elements are used toindicate the determined MVD precision from the set of allowed multipleMVD precisions applied to both the affine mode and a non-affine mode.

9. The method of clause 3, 7, or 8, wherein the affine mode and thenon-affine mode use a same set of the allowed multiple MVD precisions.

10. The method of clause 3, 7, or 8, wherein the affine coded blocks usea different set of the allowed multiple MVD precisions from that used ina non-affine mode.

11. The method of clause 10, wherein the different set having a samenumber of the allowed multiple MVD precisions as that used in thenon-affine mode, the syntax elements used in the non-affine mode arereused in the affine mode.

12. The method of clause 10, wherein the different set has at least oneMVD precision that is different from that used in the non-affine mode.

13. The method of clause 3, 7, or 8, wherein semantics of syntaxelements used in the non-affine mode and the affine mode are differentand the syntax elements have a same decoded value interpreted todifferent MVD precisions.

14. The method of clause 3, 7, or 8, wherein a number of the allowedmultiple MVD precisions used in the affine mode is less than that usedin a non-affine mode.

15. The method of clause 8, wherein one or more subsets of the syntaxvalues for the non-affine mode are not valid in the affine mode.

16. The method of claim 8 or 14, wherein semantics of syntax elementsused in the non-affine mode and the affine mode are different and thesyntax elements with same value is interpreted to different MVDprecisions.

17. The method of clause 3 or 7, wherein a number of the allowedmultiple MVD precisions used in the affine mode is more than that usedin a non-affine mode

18. The method of clause 17, wherein one or more syntax elements in thenon-affine mode are extended to allow more values for the affine mode.

19. The method of clause 7, wherein an additional syntax element is usedfor processing the MVD precision of the affine mode, the additionalsyntax element being different from that used for processing the MVDprecision of a non-affine mode.

20. The method of clause 7, wherein indication of the MVD precision forthe affine mode is selectively signaled.

21. The method of clause 20, wherein indication of the MVD precision forthe affine mode is signaled when MVDs for all control point motionvectors (CPMVs) are non-zero.

22. The method of clause 20, wherein indication of the MVD precision forthe affine mode is signaled when MVDs for at least one CPMV is non-zero.

23. The method of clause 20, wherein indication of the MVD precision forthe affine mode is signaled when MVD of one selected CPMV is non-zero.

24. The method of clause 20, wherein indication of the MVD precision forthe affine mode is signaled when MVD of a first CPMV is non-zero.

25. The method of clause 20, wherein indication of the MVD precision forthe affine mode is not signaled when one or more predeterminedconditions are not satisfied.

26. The method of clause 7, wherein a syntax element for MVD precisionindications associated with either the affine mode or a non-affine modeis coded with contexts that are dependent on coded information of thecurrent block.

27. The method of clause 7, wherein a context selection of the syntaxelement for MVD precision indications associated with either the affinemode or a non-affine mode is dependent on whether the current block iscoded with affine mode or not.

28. The method of clause 7, wherein one context is used for the syntaxelement for MVD precision indications for an affine coded block andanother context is used for a non-affine coded block.

29. The method of clause 7, wherein a context for MVD precisionindications is determined based on a size, shape, or MVD precisions ofneighboring blocks, a temporal layer index, or prediction directions.

30. The method of clause 7, wherein whether to enable or disable a usageof the allowed multiple MVD precisions for the affine mode is signaledin a sequence parameter set (SPS), a picture parameter set (PPS), avideo parameter set (VPS), a sequence header, a picture header, a sliceheader, or a group of coding tree units (CTUs).

31. The method of clause 7, wherein whether to enable or disable a usageof the allowed multiple MVD precisions for the affine mode depends onthe one or more syntax elements.

32. The method of clause 7, wherein information whether to enable ordisable a usage of the allowed multiple MVD precisions is signaled uponan enablement of the affine mode and is not signaled upon a disablementof the affine mode.

33. The method of any of clauses 7 to 32, wherein the one or more syntaxelements are included at a slice level, a picture level, or sequencelevel.

34. The method of clause 5, 30, or 33, wherein the slice is replacedwith a tile group or tile.

35. The method of any of clauses 1 to 34, wherein, in a VPS, SPS, PPS,slice header, or tile group header, a syntax element equal to 1specifies a requirement to conform the coded representation, therequirement requiring that both of a first syntax element to indicatewhether a first set of multiple MVD precisions is enabled for anon-affine mode and a second syntax element to indicate whether a secondset of multiple MVD precisions is enabled for the affine-mode are 0.

36. The method of any of clauses 1 to 34, wherein a syntax element issignaled in a VPS, SPS, PPS, slice header, tile group header, or othervideo data units,

37. The method of clause 36, wherein the syntax element equal to 1specifies a requirement to conform the coded representation, therequirement requiring that the syntax element to indicate whethermultiple MVD precisions is enabled for the affine mode is equal to 0.

38. The method of any of clauses 7 to 37, wherein a motion vectorpredictor is utilized in a same MVD precision for affine coded blocks.

39. The method of any of clauses 7 to 37, wherein a final motion vectorof the current block is utilized in a same MVD precision for affinecoded blocks.

40. The method of any of clauses 1 to 39, wherein the performing of theconversion includes generating the coded representation from the currentblock.

41. The method of any of clauses 1 to 39, wherein the performing of theconversion includes generating the current block from the codedrepresentation.

42. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of clauses 1 to 41.

43. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of clauses 1 to 41.

The second set of clauses use some of the techniques described in theprevious section, including, for example, items 3, 4, and 12 in theprevious section.

1. A method of video processing, comprising: determining, for a videoregion comprising one or more video blocks of a video and a codedrepresentation of the video, a usage of multiple motion vectordifference (MVD) precisions for the conversion of the one or more videoblocks in the video region; and performing the conversion based on thedetermining.

2. The method of clause 1, wherein the conversion of at least some ofthe one or more video blocks is based on affine mode coding.

3. The method of clause 1 or 2, wherein the usage is indicated in thecoded representation including a Sequence Parameter Set (SPS), a PictureParameter Set (PPS), a Video Parameter Set (VPS), a sequence header, apicture header, a slice header, or a group of coding tree units (CTUs)

4. The method of clause 3, wherein the usage is indicated depending on asyntax element used to indicate the MVD precisions.

5. A method of video processing, comprising: determining, for a videoregion comprising one or more video blocks of a video and a codedrepresentation of the video, whether to apply an adaptive motion vectorresolution (AMVR) process to a current video block for a conversionbetween the current video block and the coded representation of thevideo; and performing the conversion based on the determining.

6. A method of video processing, comprising: determining, for a videoregion comprising one or more video blocks of a video and a codedrepresentation of the video, how to apply an adaptive motion vectorresolution (AMVR) process to a current video block for a conversionbetween the current video block and the coded representation of thevideo; and performing the conversion based on the determining.

7. The method of clause 5 or 6, wherein the conversion of the currentvideo block is based on affine mode coding.

8. The method of clause 7, wherein the determining depends on areference picture of the current video block.

9. The method of clause 8, wherein, in a case that the reference pictureis a current picture, the determining determines not to apply the AMVRprocess.

10. The method of clause 5 or 6, wherein the determining depends onwhether an intra block copying (IBC) is applied to the current block ornot.

11. The method of clause 10, wherein the determining determines to applythe AMVR process to the current block coded by the IBC.

12. the method of clause 11, wherein candidate MV (motion vector), MVD,or MVP (motion vector prediction) precisions for IBC coded blocks aredifferent from those used for another video block not coded by the IBC.

13. the method of clause 11, wherein candidate MV (motion vector), MVD,or MVP (motion vector prediction) precisions for IBC coded blocks aredifferent from those used for another video block coded with affinemode.

14. The method of any of clauses 1 to 13, wherein the performing of theconversion includes generating the coded representation from the currentblock.

15. The method of any of clauses 1 to 13, wherein the performing of theconversion includes generating the current block from the codedrepresentation.

16. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of clauses 1 to 15.

17. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of clauses 1 to 15.

The third set of clauses use some of the techniques described in theprevious section, including, for example, items 5-10 and 13 in theprevious section.

1. A method of video processing, comprising: determining, based on acoding mode of a parent coding unit of a current coding unit that usesan affine coding mode or a rate-distortion (RD) cost of the affinecoding mode, a usage of an adaptive motion vector resolution (AMVR) fora conversion between a coded representation of a current block of avideo and the current block; and performing the conversion according toa result of the determining.

2. The method of clause 1, wherein, in case that the coding mode of theparent coding unit is not AF_Inter mode or AF_MERGE mode, then thedetermining disables the usage of the AMVR for the current coding unit.

3. The method of clause 1, wherein, in case that the coding mode of theparent coding unit is not AF_Inter mode, then the determining disablesthe usage of the AMVR for the current coding unit.

4. The method of clause 1, wherein, in case that the RD of the affinecoding mode is greater than a multiplication of a positive threshold andan RD cost of an advanced motion vector prediction (AMVP) mode, then thedetermining disables the usage of the AMVR for the current coding unit.

5. The method of clause 4, wherein the determination is applied for¼-pel MV precision.

6. The method of clause 1, wherein, in case that a minimum RD cost isgreater than a multiplication of a positive threshold and an RD cost ofa merge mode, then the determining disables the usage of the AMVR forthe current coding unit, wherein the minimum RD cost is a minimum of theRD cost of the affine coding mode and an RD cost of an advanced motionvector prediction (AMVP) mode.

7. The method of clause 6, wherein the determination is applied for¼-pel MV precision.

8. A method of video processing, comprising: determining a usage of anadaptive motion vector resolution (AMVR) for a conversion between acoded representation of a current block of a video and the current blockthat uses an advanced motion vector prediction (AMVP) coding mode, thedetermining based on a rate-distortion (RD) cost of the AMVP codingmode; and performing the conversion according to a result of thedetermining.

9. The method of clause 8, wherein, in case that the RD cost of the AMVPcoding mode is greater than a multiplication of a positive threshold andan RD cost of an affine mode, the determining disables the usage of theAMVR.

10. The method of clause 8, wherein the determination is applied for¼-pel MV precision.

11. The method of clause 8, wherein, in case that a minimum RD cost isgreater than a multiplication of a positive threshold and an RD cost ofa merge mode, the determining disables the usage of the AMVR, andwherein the minimum RD cost is a minimum of an RD cost of an affine modeand an RD cost of the AMVP coding mode.

12. The method of clause 11, wherein the determination is applied for¼-pel MV precision.

13. A method of video processing, comprising: generating, for aconversion between a coded representation of a current block of a videoand the current block, a set of MV (Motion Vector) precisions using a4-parameter affine model or 6-parameter affine model; and performing theconversion based on the set of MV precisions.

14. The method of clause 13, wherein the 4-parameter affine model or the6-parameter affine model obtained in a single MV precision is used as acandidate start search point for other MV precisions.

15. The method of clause 14, wherein the single MV precision comprises1/16 MV accuracy.

16. The method of clause 14, wherein the single MV precision comprises ¼MV accuracy.

17. A method of video processing, comprising: determining, based on acoding mode of a parent block of a current block that uses an affinecoding mode, whether an adaptive motion vector resolution (AMVR) tool isused for a conversion, wherein the AMVR tool is used to refine motionvector resolution during decoding; and performing the conversionaccording to a result of the determining.

18. The method of clause 17, wherein, in case that the parent block ofthe current block is not the affine coding mode, the determining causesnot to check the AMVR for the current block.

19. A method of video processing, comprising: determining, based on ausage of MV precisions for previous blocks that has been previouslycoded using an affine coding mode, a termination of a rate-distortion(RD) calculations of MV precisions for a current block that uses theaffine coding mode for a conversion between a coded representation ofthe current block and the current block; and performing the conversionaccording to a result of the determining.

20. The method of clause 19, wherein the current block and the previousblocks are included in a current image segment and a previous imagesegment, respectively, and the current image segment and the previousimage segments are pictures, slices, tiles, or CTU (Coding Tree Unit)rows.

21. The method of any of clauses 1 to 20, wherein the performing of theconversion includes generating the coded representation from the currentblock.

22. The method of any of clauses 1 to 20, wherein the performing of theconversion includes generating the current block from the codedrepresentation.

23. An apparatus in a video system comprising a processor and anon-transitory memory with instructions thereon, wherein theinstructions upon execution by the processor, cause the processor toimplement the method in any one of clauses 1 to 22.

24. A computer program product stored on a non-transitory computerreadable media, the computer program product including program code forcarrying out the method in any one of claims 1 to 22.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the scope of the invention. Accordingly, thepresently disclosed technology is not limited except as by the appendedclaims.

Implementations of the subject matter and the functional operationsdescribed in this patent document can be implemented in various systems,digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.Implementations of the subject matter described in this specificationcan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on a tangibleand non-transitory computer readable medium for execution by, or tocontrol the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing unit” or “dataprocessing apparatus” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Theapparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

It is intended that the specification, together with the drawings, beconsidered exemplary only, where exemplary means an example. As usedherein, the use of “or” is intended to include “and/or”, unless thecontext clearly indicates otherwise.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of video processing, comprising:generating, for a conversion between a coded representation of a currentblock of a video and the current block, a set of MV (Motion Vector)precisions using a 4-parameter affine model or 6-parameter affine model;and performing the conversion based on the set of MV precisions.
 2. Themethod of claim 1, wherein the 4-parameter affine model or the6-parameter affine model obtained in a single MV precision is used as acandidate start search point for other MV precisions.
 3. The method ofclaim 2, wherein the single MV precision comprises 1/16 MV accuracy or ¼MV accuracy.
 4. The method of claim 2, wherein the single MV precisioncomprises ¼ MV accuracy.
 5. The method of claim 1, the method furthercomprising: determining, based on a coding mode of a parent block of acurrent block that uses an affine coding mode, whether an adaptivemotion vector resolution (AMVR) tool is used for the conversion, whereinthe AMVR tool is used to refine motion vector resolution duringdecoding; and performing the conversion according to a result of thedetermining and the set of MV precisions.
 6. The method of claim 5,wherein, in case that the parent block of the current block is not codedwith the affine coding mode, the determining causes not to check theAMVR for the current block.
 7. The method of claim 1, the method furthercomprising: determining, based on a usage of MV precisions for previousblocks that has been previously coded using an affine coding mode, atermination of a rate-distortion (RD) calculations of MV precisions fora current block that uses the affine coding mode for the conversionbetween the coded representation of the current block of the video andthe current block; and performing the conversion according to a resultof the determining and the set of MV precisions.
 8. The method of claim7, wherein the current block and the previous blocks are included in acurrent image segment and a previous image segment, respectively, andthe current image segment and the previous image segments are pictures,slices, tiles, or CTU (Coding Tree Unit) rows.
 9. The method of claim 1,the method further comprising: determining, based on a coding mode of aparent coding unit of a current coding unit that uses an affine codingmode or a rate-distortion (RD) cost of the affine coding mode, a usageof an adaptive motion vector resolution (AMVR) for the conversionbetween the coded representation of the current block of the video andthe current block; and performing the conversion according to a resultof the determining and the set of MV precisions.
 10. The method of claim9, wherein, in case that the coding mode of the parent coding unit isnot AF_Inter mode or AF_MERGE mode, then the determining disables theusage of the AMVR for the current coding unit.
 11. The method of claim9, wherein, in case that the RD of the affine coding mode is greaterthan a multiplication of a positive threshold and an RD cost of anadvanced motion vector prediction (AMVP) mode, then the determiningdisables the usage of the AMVR for the current coding unit.
 12. Themethod of claim 11, wherein the determination is applied for ¼-pel MVprecision.
 13. The method of claim 9, wherein, in case that a minimum RDcost is greater than a multiplication of a positive threshold and an RDcost of a merge mode, then the determining disables the usage of theAMVR for the current coding unit, wherein the minimum RD cost is aminimum of the RD cost of the affine coding mode and an RD cost of anadvanced motion vector prediction (AMVP) mode.
 14. The method of claim1, the method further comprising: determining a usage of an adaptivemotion vector resolution (AMVR) for the conversion between the codedrepresentation of the current block of the video and the current blockthat uses an advanced motion vector prediction (AMVP) coding mode, thedetermining based on a rate-distortion (RD) cost of the AMVP codingmode; and performing the conversion according to a result of thedetermining and the set of MV precisions.
 15. The method of claim 14,wherein, in case that the RD cost of the AMVP coding mode is greaterthan a multiplication of a positive threshold and an RD cost of anaffine mode, the determining disables the usage of the AMVR.
 16. Themethod of claim 14, wherein, in case that a minimum RD cost is greaterthan a multiplication of a positive threshold and an RD cost of a mergemode, the determining disables the usage of the AMVR, and wherein theminimum RD cost is a minimum of an RD cost of an affine mode and an RDcost of the AMVP coding mode.
 17. The method of claim 1, wherein theperforming of the conversion includes generating the codedrepresentation from the current block.
 18. The method of claim 1,wherein the performing of the conversion includes generating the currentblock from the coded representation.
 19. An apparatus in a video systemcomprising a processor and a non-transitory memory with instructionsthereon, wherein the instructions upon execution by the processor, causethe processor to implement the method recited in claim
 1. 20. A computerprogram product stored on a non-transitory computer readable media, thecomputer program product including program code for carrying out themethod recited in claim 1.